diff --git a/packages/babel-plugin-transform-typescript/src/index.js b/packages/babel-plugin-transform-typescript/src/index.js
index 29afc79cf112..8a8ca8bfd778 100644
--- a/packages/babel-plugin-transform-typescript/src/index.js
+++ b/packages/babel-plugin-transform-typescript/src/index.js
@@ -4,6 +4,7 @@ import { types as t, template } from "@babel/core";
 import { injectInitialization } from "@babel/helper-create-class-features-plugin";
 
 import transpileEnum from "./enum";
+import transpileNamespace from "./namespace";
 
 function isInType(path) {
   switch (path.parent.type) {
@@ -24,331 +25,333 @@ interface State {
 const PARSED_PARAMS = new WeakSet();
 const PRAGMA_KEY = "@babel/plugin-transform-typescript/jsxPragma";
 
-export default declare((api, { jsxPragma = "React" }) => {
-  api.assertVersion(7);
+export default declare(
+  (api, { jsxPragma = "React", allowNamespaces = false }) => {
+    api.assertVersion(7);
 
-  const JSX_ANNOTATION_REGEX = /\*?\s*@jsx\s+([^\s]+)/;
+    const JSX_ANNOTATION_REGEX = /\*?\s*@jsx\s+([^\s]+)/;
 
-  return {
-    name: "transform-typescript",
-    inherits: syntaxTypeScript,
+    return {
+      name: "transform-typescript",
+      inherits: syntaxTypeScript,
 
-    visitor: {
-      //"Pattern" alias doesn't include Identifier or RestElement.
-      Pattern: visitPattern,
-      Identifier: visitPattern,
-      RestElement: visitPattern,
+      visitor: {
+        //"Pattern" alias doesn't include Identifier or RestElement.
+        Pattern: visitPattern,
+        Identifier: visitPattern,
+        RestElement: visitPattern,
 
-      Program(path, state: State) {
-        state.programPath = path;
+        Program(path, state: State) {
+          state.programPath = path;
 
-        const { file } = state;
+          const { file } = state;
 
-        if (file.ast.comments) {
-          for (const comment of (file.ast.comments: Array<Object>)) {
-            const jsxMatches = JSX_ANNOTATION_REGEX.exec(comment.value);
-            if (jsxMatches) {
-              file.set(PRAGMA_KEY, jsxMatches[1]);
+          if (file.ast.comments) {
+            for (const comment of (file.ast.comments: Array<Object>)) {
+              const jsxMatches = JSX_ANNOTATION_REGEX.exec(comment.value);
+              if (jsxMatches) {
+                file.set(PRAGMA_KEY, jsxMatches[1]);
+              }
             }
           }
-        }
 
-        // remove type imports
-        for (const stmt of path.get("body")) {
-          if (t.isImportDeclaration(stmt)) {
-            // Note: this will allow both `import { } from "m"` and `import "m";`.
-            // In TypeScript, the former would be elided.
-            if (stmt.node.specifiers.length === 0) {
-              continue;
-            }
+          // remove type imports
+          for (const stmt of path.get("body")) {
+            if (t.isImportDeclaration(stmt)) {
+              // Note: this will allow both `import { } from "m"` and `import "m";`.
+              // In TypeScript, the former would be elided.
+              if (stmt.node.specifiers.length === 0) {
+                continue;
+              }
 
-            let allElided = true;
-            const importsToRemove: Path<Node>[] = [];
-
-            for (const specifier of stmt.node.specifiers) {
-              const binding = stmt.scope.getBinding(specifier.local.name);
-
-              // The binding may not exist if the import node was explicitly
-              // injected by another plugin. Currently core does not do a good job
-              // of keeping scope bindings synchronized with the AST. For now we
-              // just bail if there is no binding, since chances are good that if
-              // the import statement was injected then it wasn't a typescript type
-              // import anyway.
-              if (
-                binding &&
-                isImportTypeOnly(file, binding, state.programPath)
-              ) {
-                importsToRemove.push(binding.path);
-              } else {
-                allElided = false;
+              let allElided = true;
+              const importsToRemove: Path<Node>[] = [];
+
+              for (const specifier of stmt.node.specifiers) {
+                const binding = stmt.scope.getBinding(specifier.local.name);
+
+                // The binding may not exist if the import node was explicitly
+                // injected by another plugin. Currently core does not do a good job
+                // of keeping scope bindings synchronized with the AST. For now we
+                // just bail if there is no binding, since chances are good that if
+                // the import statement was injected then it wasn't a typescript type
+                // import anyway.
+                if (
+                  binding &&
+                  isImportTypeOnly(file, binding, state.programPath)
+                ) {
+                  importsToRemove.push(binding.path);
+                } else {
+                  allElided = false;
+                }
               }
-            }
 
-            if (allElided) {
-              stmt.remove();
-            } else {
-              for (const importPath of importsToRemove) {
-                importPath.remove();
+              if (allElided) {
+                stmt.remove();
+              } else {
+                for (const importPath of importsToRemove) {
+                  importPath.remove();
+                }
               }
             }
           }
-        }
-      },
+        },
+
+        ExportNamedDeclaration(path) {
+          // remove export declaration if it's exporting only types
+          if (
+            path.node.specifiers.length > 0 &&
+            !path.node.specifiers.find(exportSpecifier =>
+              path.scope.hasOwnBinding(exportSpecifier.local.name),
+            )
+          ) {
+            path.remove();
+          }
+        },
 
-      ExportNamedDeclaration(path) {
-        // remove export declaration if it's exporting only types
-        if (
-          path.node.specifiers.length > 0 &&
-          !path.node.specifiers.find(exportSpecifier =>
-            path.scope.hasOwnBinding(exportSpecifier.local.name),
-          )
-        ) {
-          path.remove();
-        }
-      },
+        ExportSpecifier(path) {
+          // remove type exports
+          if (!path.scope.hasOwnBinding(path.node.local.name)) {
+            path.remove();
+          }
+        },
+
+        ExportDefaultDeclaration(path) {
+          // remove whole declaration if it's exporting a TS type
+          if (
+            t.isIdentifier(path.node.declaration) &&
+            !path.scope.hasOwnBinding(path.node.declaration.name)
+          ) {
+            path.remove();
+          }
+        },
 
-      ExportSpecifier(path) {
-        // remove type exports
-        if (!path.scope.hasOwnBinding(path.node.local.name)) {
+        TSDeclareFunction(path) {
           path.remove();
-        }
-      },
+        },
 
-      ExportDefaultDeclaration(path) {
-        // remove whole declaration if it's exporting a TS type
-        if (
-          t.isIdentifier(path.node.declaration) &&
-          !path.scope.hasOwnBinding(path.node.declaration.name)
-        ) {
+        TSDeclareMethod(path) {
           path.remove();
-        }
-      },
+        },
 
-      TSDeclareFunction(path) {
-        path.remove();
-      },
+        VariableDeclaration(path) {
+          if (path.node.declare) path.remove();
+        },
 
-      TSDeclareMethod(path) {
-        path.remove();
-      },
+        VariableDeclarator({ node }) {
+          if (node.definite) node.definite = null;
+        },
 
-      VariableDeclaration(path) {
-        if (path.node.declare) path.remove();
-      },
+        ClassMethod(path) {
+          const { node } = path;
 
-      VariableDeclarator({ node }) {
-        if (node.definite) node.definite = null;
-      },
+          if (node.accessibility) node.accessibility = null;
+          if (node.abstract) node.abstract = null;
+          if (node.optional) node.optional = null;
 
-      ClassMethod(path) {
-        const { node } = path;
+          // Rest handled by Function visitor
+        },
 
-        if (node.accessibility) node.accessibility = null;
-        if (node.abstract) node.abstract = null;
-        if (node.optional) node.optional = null;
+        ClassProperty(path) {
+          const { node } = path;
 
-        // Rest handled by Function visitor
-      },
-
-      ClassProperty(path) {
-        const { node } = path;
-
-        if (node.accessibility) node.accessibility = null;
-        if (node.abstract) node.abstract = null;
-        if (node.readonly) node.readonly = null;
-        if (node.optional) node.optional = null;
-        if (node.definite) node.definite = null;
-        if (node.typeAnnotation) node.typeAnnotation = null;
-      },
-
-      TSIndexSignature(path) {
-        path.remove();
-      },
+          if (node.accessibility) node.accessibility = null;
+          if (node.abstract) node.abstract = null;
+          if (node.readonly) node.readonly = null;
+          if (node.optional) node.optional = null;
+          if (node.definite) node.definite = null;
+          if (node.typeAnnotation) node.typeAnnotation = null;
+        },
 
-      ClassDeclaration(path) {
-        const { node } = path;
-        if (node.declare) {
+        TSIndexSignature(path) {
           path.remove();
-          return;
-        }
-      },
-
-      Class(path) {
-        const { node } = path;
-
-        if (node.typeParameters) node.typeParameters = null;
-        if (node.superTypeParameters) node.superTypeParameters = null;
-        if (node.implements) node.implements = null;
-        if (node.abstract) node.abstract = null;
-
-        // Similar to the logic in `transform-flow-strip-types`, we need to
-        // handle `TSParameterProperty` and `ClassProperty` here because the
-        // class transform would transform the class, causing more specific
-        // visitors to not run.
-        path.get("body.body").forEach(child => {
-          const childNode = child.node;
-
-          if (t.isClassMethod(childNode, { kind: "constructor" })) {
-            // Collects parameter properties so that we can add an assignment
-            // for each of them in the constructor body
-            //
-            // We use a WeakSet to ensure an assignment for a parameter
-            // property is only added once. This is necessary for cases like
-            // using `transform-classes`, which causes this visitor to run
-            // twice.
-            const parameterProperties = [];
-            for (const param of childNode.params) {
-              if (
-                param.type === "TSParameterProperty" &&
-                !PARSED_PARAMS.has(param.parameter)
-              ) {
-                PARSED_PARAMS.add(param.parameter);
-                parameterProperties.push(param.parameter);
-              }
-            }
+        },
 
-            if (parameterProperties.length) {
-              const assigns = parameterProperties.map(p => {
-                let id;
-                if (t.isIdentifier(p)) {
-                  id = p;
-                } else if (t.isAssignmentPattern(p) && t.isIdentifier(p.left)) {
-                  id = p.left;
-                } else {
-                  throw path.buildCodeFrameError(
-                    "Parameter properties can not be destructuring patterns.",
-                  );
+        ClassDeclaration(path) {
+          const { node } = path;
+          if (node.declare) {
+            path.remove();
+            return;
+          }
+        },
+
+        Class(path) {
+          const { node } = path;
+
+          if (node.typeParameters) node.typeParameters = null;
+          if (node.superTypeParameters) node.superTypeParameters = null;
+          if (node.implements) node.implements = null;
+          if (node.abstract) node.abstract = null;
+
+          // Similar to the logic in `transform-flow-strip-types`, we need to
+          // handle `TSParameterProperty` and `ClassProperty` here because the
+          // class transform would transform the class, causing more specific
+          // visitors to not run.
+          path.get("body.body").forEach(child => {
+            const childNode = child.node;
+
+            if (t.isClassMethod(childNode, { kind: "constructor" })) {
+              // Collects parameter properties so that we can add an assignment
+              // for each of them in the constructor body
+              //
+              // We use a WeakSet to ensure an assignment for a parameter
+              // property is only added once. This is necessary for cases like
+              // using `transform-classes`, which causes this visitor to run
+              // twice.
+              const parameterProperties = [];
+              for (const param of childNode.params) {
+                if (
+                  param.type === "TSParameterProperty" &&
+                  !PARSED_PARAMS.has(param.parameter)
+                ) {
+                  PARSED_PARAMS.add(param.parameter);
+                  parameterProperties.push(param.parameter);
                 }
+              }
 
-                return template.statement.ast`this.${id} = ${id}`;
-              });
-
-              injectInitialization(path, child, assigns);
-            }
-          } else if (child.isClassProperty()) {
-            childNode.typeAnnotation = null;
+              if (parameterProperties.length) {
+                const assigns = parameterProperties.map(p => {
+                  let id;
+                  if (t.isIdentifier(p)) {
+                    id = p;
+                  } else if (
+                    t.isAssignmentPattern(p) &&
+                    t.isIdentifier(p.left)
+                  ) {
+                    id = p.left;
+                  } else {
+                    throw path.buildCodeFrameError(
+                      "Parameter properties can not be destructuring patterns.",
+                    );
+                  }
+
+                  return template.statement.ast`this.${id} = ${id}`;
+                });
+
+                injectInitialization(path, child, assigns);
+              }
+            } else if (child.isClassProperty()) {
+              childNode.typeAnnotation = null;
 
-            if (!childNode.value && !childNode.decorators) {
-              child.remove();
+              if (!childNode.value && !childNode.decorators) {
+                child.remove();
+              }
             }
-          }
-        });
-      },
-
-      Function({ node }) {
-        if (node.typeParameters) node.typeParameters = null;
-        if (node.returnType) node.returnType = null;
+          });
+        },
 
-        const p0 = node.params[0];
-        if (p0 && t.isIdentifier(p0) && p0.name === "this") {
-          node.params.shift();
-        }
-
-        // We replace `TSParameterProperty` here so that transforms that
-        // rely on a `Function` visitor to deal with arguments, like
-        // `transform-parameters`, work properly.
-        node.params = node.params.map(p => {
-          return p.type === "TSParameterProperty" ? p.parameter : p;
-        });
-      },
-
-      TSModuleDeclaration(path) {
-        if (!path.node.declare && path.node.id.type !== "StringLiteral") {
-          throw path.buildCodeFrameError("Namespaces are not supported.");
-        }
-        path.remove();
-      },
-
-      TSInterfaceDeclaration(path) {
-        path.remove();
-      },
-
-      TSTypeAliasDeclaration(path) {
-        path.remove();
-      },
-
-      TSEnumDeclaration(path) {
-        transpileEnum(path, t);
-      },
-
-      TSImportEqualsDeclaration(path) {
-        throw path.buildCodeFrameError(
-          "`import =` is not supported by @babel/plugin-transform-typescript\n" +
-            "Please consider using " +
-            "`import <moduleName> from '<moduleName>';` alongside " +
-            "Typescript's --allowSyntheticDefaultImports option.",
-        );
-      },
-
-      TSExportAssignment(path) {
-        throw path.buildCodeFrameError(
-          "`export =` is not supported by @babel/plugin-transform-typescript\n" +
-            "Please consider using `export <value>;`.",
-        );
-      },
+        Function({ node }) {
+          if (node.typeParameters) node.typeParameters = null;
+          if (node.returnType) node.returnType = null;
 
-      TSTypeAssertion(path) {
-        path.replaceWith(path.node.expression);
-      },
-
-      TSAsExpression(path) {
-        let { node } = path;
-        do {
-          node = node.expression;
-        } while (t.isTSAsExpression(node));
-        path.replaceWith(node);
-      },
+          const p0 = node.params[0];
+          if (p0 && t.isIdentifier(p0) && p0.name === "this") {
+            node.params.shift();
+          }
 
-      TSNonNullExpression(path) {
-        path.replaceWith(path.node.expression);
-      },
+          // We replace `TSParameterProperty` here so that transforms that
+          // rely on a `Function` visitor to deal with arguments, like
+          // `transform-parameters`, work properly.
+          node.params = node.params.map(p => {
+            return p.type === "TSParameterProperty" ? p.parameter : p;
+          });
+        },
 
-      CallExpression(path) {
-        path.node.typeParameters = null;
-      },
+        TSModuleDeclaration(path) {
+          transpileNamespace(path, t, allowNamespaces);
+        },
 
-      NewExpression(path) {
-        path.node.typeParameters = null;
-      },
+        TSInterfaceDeclaration(path) {
+          path.remove();
+        },
 
-      JSXOpeningElement(path) {
-        path.node.typeParameters = null;
+        TSTypeAliasDeclaration(path) {
+          path.remove();
+        },
+
+        TSEnumDeclaration(path) {
+          transpileEnum(path, t);
+        },
+
+        TSImportEqualsDeclaration(path) {
+          throw path.buildCodeFrameError(
+            "`import =` is not supported by @babel/plugin-transform-typescript\n" +
+              "Please consider using " +
+              "`import <moduleName> from '<moduleName>';` alongside " +
+              "Typescript's --allowSyntheticDefaultImports option.",
+          );
+        },
+
+        TSExportAssignment(path) {
+          throw path.buildCodeFrameError(
+            "`export =` is not supported by @babel/plugin-transform-typescript\n" +
+              "Please consider using `export <value>;`.",
+          );
+        },
+
+        TSTypeAssertion(path) {
+          path.replaceWith(path.node.expression);
+        },
+
+        TSAsExpression(path) {
+          let { node } = path;
+          do {
+            node = node.expression;
+          } while (t.isTSAsExpression(node));
+          path.replaceWith(node);
+        },
+
+        TSNonNullExpression(path) {
+          path.replaceWith(path.node.expression);
+        },
+
+        CallExpression(path) {
+          path.node.typeParameters = null;
+        },
+
+        NewExpression(path) {
+          path.node.typeParameters = null;
+        },
+
+        JSXOpeningElement(path) {
+          path.node.typeParameters = null;
+        },
+
+        TaggedTemplateExpression(path) {
+          path.node.typeParameters = null;
+        },
       },
+    };
 
-      TaggedTemplateExpression(path) {
-        path.node.typeParameters = null;
-      },
-    },
-  };
+    function visitPattern({ node }) {
+      if (node.typeAnnotation) node.typeAnnotation = null;
+      if (t.isIdentifier(node) && node.optional) node.optional = null;
+      // 'access' and 'readonly' are only for parameter properties, so constructor visitor will handle them.
+    }
 
-  function visitPattern({ node }) {
-    if (node.typeAnnotation) node.typeAnnotation = null;
-    if (t.isIdentifier(node) && node.optional) node.optional = null;
-    // 'access' and 'readonly' are only for parameter properties, so constructor visitor will handle them.
-  }
+    function isImportTypeOnly(file, binding, programPath) {
+      for (const path of binding.referencePaths) {
+        if (!isInType(path)) {
+          return false;
+        }
+      }
 
-  function isImportTypeOnly(file, binding, programPath) {
-    for (const path of binding.referencePaths) {
-      if (!isInType(path)) {
-        return false;
+      const fileJsxPragma = file.get(PRAGMA_KEY) || jsxPragma;
+      if (binding.identifier.name !== fileJsxPragma) {
+        return true;
       }
-    }
 
-    const fileJsxPragma = file.get(PRAGMA_KEY) || jsxPragma;
-    if (binding.identifier.name !== fileJsxPragma) {
-      return true;
+      // "React" or the JSX pragma is referenced as a value if there are any JSX elements in the code.
+      let sourceFileHasJsx = false;
+      programPath.traverse({
+        JSXElement() {
+          sourceFileHasJsx = true;
+        },
+        JSXFragment() {
+          sourceFileHasJsx = true;
+        },
+      });
+      return !sourceFileHasJsx;
     }
-
-    // "React" or the JSX pragma is referenced as a value if there are any JSX elements in the code.
-    let sourceFileHasJsx = false;
-    programPath.traverse({
-      JSXElement() {
-        sourceFileHasJsx = true;
-      },
-      JSXFragment() {
-        sourceFileHasJsx = true;
-      },
-    });
-    return !sourceFileHasJsx;
-  }
-});
+  },
+);
diff --git a/packages/babel-plugin-transform-typescript/src/namespace.js b/packages/babel-plugin-transform-typescript/src/namespace.js
new file mode 100644
index 000000000000..32d53447a80a
--- /dev/null
+++ b/packages/babel-plugin-transform-typescript/src/namespace.js
@@ -0,0 +1,171 @@
+import { template } from "@babel/core";
+
+export default function transpileNamespace(path, t, allowNamespaces) {
+  if (path.node.declare || path.node.id.type === "StringLiteral") {
+    path.remove();
+    return;
+  }
+
+  if (!allowNamespaces) {
+    throw path.hub.file.buildCodeFrameError(
+      path.node.id,
+      "Namespace not marked type-only declare." +
+        " Non-declarative namespaces are only supported experimentally in Babel." +
+        " To enable and review caveats see:" +
+        " https://babeljs.io/docs/en/babel-plugin-transform-typescript",
+    );
+  }
+
+  const name = path.node.id.name;
+  const value = handleNested(path, t, t.cloneDeep(path.node));
+  const bound = path.scope.hasOwnBinding(name);
+  if (path.parent.type === "ExportNamedDeclaration") {
+    if (!bound) {
+      path.parentPath.insertAfter(value);
+      path.replaceWith(getDeclaration(t, name));
+      path.scope.registerDeclaration(path.parentPath);
+    } else {
+      path.parentPath.replaceWith(value);
+    }
+  } else if (bound) {
+    path.replaceWith(value);
+  } else {
+    path.scope.registerDeclaration(
+      path.replaceWithMultiple([getDeclaration(t, name), value])[0],
+    );
+  }
+}
+
+function getDeclaration(t, name) {
+  return t.variableDeclaration("let", [
+    t.variableDeclarator(t.identifier(name)),
+  ]);
+}
+
+function getMemberExpression(t, name, itemName) {
+  return t.memberExpression(t.identifier(name), t.identifier(itemName));
+}
+
+function handleNested(path, t, node, parentExport) {
+  const names = new Set();
+  const realName = node.id;
+  const name = path.scope.generateUid(realName.name);
+  const namespaceTopLevel = node.body.body;
+  for (let i = 0; i < namespaceTopLevel.length; i++) {
+    const subNode = namespaceTopLevel[i];
+
+    // The first switch is mainly to detect name usage. Only export
+    // declarations require further transformation.
+    switch (subNode.type) {
+      case "TSModuleDeclaration": {
+        const transformed = handleNested(path, t, subNode);
+        const moduleName = subNode.id.name;
+        if (names.has(moduleName)) {
+          namespaceTopLevel[i] = transformed;
+        } else {
+          names.add(moduleName);
+          namespaceTopLevel.splice(
+            i++,
+            1,
+            getDeclaration(t, moduleName),
+            transformed,
+          );
+        }
+        continue;
+      }
+      case "TSEnumDeclaration":
+      case "FunctionDeclaration":
+      case "ClassDeclaration":
+        names.add(subNode.id.name);
+        continue;
+      case "VariableDeclaration":
+        for (const variable of subNode.declarations) {
+          names.add(variable.id.name);
+        }
+        continue;
+      default:
+        // Neither named declaration nor export, continue to next item.
+        continue;
+      case "ExportNamedDeclaration":
+      // Export declarations get parsed using the next switch.
+    }
+
+    // Transform the export declarations that occur inside of a namespace.
+    switch (subNode.declaration.type) {
+      case "TSEnumDeclaration":
+      case "FunctionDeclaration":
+      case "ClassDeclaration": {
+        const itemName = subNode.declaration.id.name;
+        names.add(itemName);
+        namespaceTopLevel.splice(
+          i++,
+          1,
+          subNode.declaration,
+          t.expressionStatement(
+            t.assignmentExpression(
+              "=",
+              getMemberExpression(t, name, itemName),
+              t.identifier(itemName),
+            ),
+          ),
+        );
+        break;
+      }
+      case "VariableDeclaration":
+        if (subNode.declaration.kind !== "const") {
+          throw path.hub.file.buildCodeFrameError(
+            subNode.declaration,
+            "Namespaces exporting non-const are not supported by Babel." +
+              " Change to const or see:" +
+              " https://babeljs.io/docs/en/babel-plugin-transform-typescript",
+          );
+        }
+        for (const variable of subNode.declaration.declarations) {
+          variable.init = t.assignmentExpression(
+            "=",
+            getMemberExpression(t, name, variable.id.name),
+            variable.init,
+          );
+        }
+        namespaceTopLevel[i] = subNode.declaration;
+        break;
+      case "TSModuleDeclaration": {
+        const transformed = handleNested(
+          path,
+          t,
+          subNode.declaration,
+          t.identifier(name),
+        );
+        const moduleName = subNode.declaration.id.name;
+        if (names.has(moduleName)) {
+          namespaceTopLevel[i] = transformed;
+        } else {
+          names.add(moduleName);
+          namespaceTopLevel.splice(
+            i++,
+            1,
+            getDeclaration(t, moduleName),
+            transformed,
+          );
+        }
+      }
+    }
+  }
+
+  // {}
+  let fallthroughValue = t.objectExpression([]);
+
+  if (parentExport) {
+    fallthroughValue = template.expression.ast`
+      ${parentExport}.${realName} || (
+        ${parentExport}.${realName} = ${fallthroughValue}
+      )
+    `;
+  }
+
+  return template.statement.ast`
+    (function (${t.identifier(name)}) {
+      ${namespaceTopLevel}
+    })(${realName} || (${realName} = ${fallthroughValue}));
+  `;
+}
diff --git a/packages/babel-plugin-transform-typescript/test/fixtures/declarations/nested-namespace/input.mjs b/packages/babel-plugin-transform-typescript/test/fixtures/declarations/nested-namespace/input.mjs
new file mode 100644
index 000000000000..8d01bb41f132
--- /dev/null
+++ b/packages/babel-plugin-transform-typescript/test/fixtures/declarations/nested-namespace/input.mjs
@@ -0,0 +1,4 @@
+; // Otherwise-empty file
+export declare namespace P {
+  export namespace C {}
+}
diff --git a/packages/babel-plugin-transform-typescript/test/fixtures/declarations/nested-namespace/output.mjs b/packages/babel-plugin-transform-typescript/test/fixtures/declarations/nested-namespace/output.mjs
new file mode 100644
index 000000000000..dab5d3d1c154
--- /dev/null
+++ b/packages/babel-plugin-transform-typescript/test/fixtures/declarations/nested-namespace/output.mjs
@@ -0,0 +1 @@
+; // Otherwise-empty file
diff --git a/packages/babel-plugin-transform-typescript/test/fixtures/namespace/canonical/input.mjs b/packages/babel-plugin-transform-typescript/test/fixtures/namespace/canonical/input.mjs
new file mode 100644
index 000000000000..58f6b5b21389
--- /dev/null
+++ b/packages/babel-plugin-transform-typescript/test/fixtures/namespace/canonical/input.mjs
@@ -0,0 +1,35 @@
+namespace Validation {
+  export interface StringValidator {
+    isAcceptable(s: string): boolean;
+  }
+
+  const lettersRegexp = /^[A-Za-z]+$/;
+  const numberRegexp = /^[0-9]+$/;
+
+  export class LettersOnlyValidator implements StringValidator {
+    constructor() {
+      console.log("1");
+    }
+    isAcceptable(s: string) {
+      return lettersRegexp.test(s);
+    }
+  }
+
+  export class ZipCodeValidator implements StringValidator {
+    isAcceptable(s: string) {
+      return s.length === 5 && numberRegexp.test(s);
+    }
+  }
+}
+
+let strings = ["Hello", "98052", "101"];
+
+let validators: { [s: string]: Validation.StringValidator; } = {};
+validators["ZIP code"] = new Validation.ZipCodeValidator();
+validators["Letters only"] = new Validation.LettersOnlyValidator();
+
+for (let s of strings) {
+  for (let name in validators) {
+    console.log(`"${ s }" - ${ validators[name].isAcceptable(s) ? "matches" : "does not match" } ${ name }`);
+  }
+}
diff --git a/packages/babel-plugin-transform-typescript/test/fixtures/namespace/canonical/output.mjs b/packages/babel-plugin-transform-typescript/test/fixtures/namespace/canonical/output.mjs
new file mode 100644
index 000000000000..f6993c98b8f4
--- /dev/null
+++ b/packages/babel-plugin-transform-typescript/test/fixtures/namespace/canonical/output.mjs
@@ -0,0 +1,39 @@
+let Validation;
+
+(function (_Validation) {
+  const lettersRegexp = /^[A-Za-z]+$/;
+  const numberRegexp = /^[0-9]+$/;
+
+  class LettersOnlyValidator {
+    constructor() {
+      console.log("1");
+    }
+
+    isAcceptable(s) {
+      return lettersRegexp.test(s);
+    }
+
+  }
+
+  _Validation.LettersOnlyValidator = LettersOnlyValidator;
+
+  class ZipCodeValidator {
+    isAcceptable(s) {
+      return s.length === 5 && numberRegexp.test(s);
+    }
+
+  }
+
+  _Validation.ZipCodeValidator = ZipCodeValidator;
+})(Validation || (Validation = {}));
+
+let strings = ["Hello", "98052", "101"];
+let validators = {};
+validators["ZIP code"] = new Validation.ZipCodeValidator();
+validators["Letters only"] = new Validation.LettersOnlyValidator();
+
+for (let s of strings) {
+  for (let name in validators) {
+    console.log(`"${s}" - ${validators[name].isAcceptable(s) ? "matches" : "does not match"} ${name}`);
+  }
+}
diff --git a/packages/babel-plugin-transform-typescript/test/fixtures/namespace/clobber-class/input.mjs b/packages/babel-plugin-transform-typescript/test/fixtures/namespace/clobber-class/input.mjs
new file mode 100644
index 000000000000..f8debe984b83
--- /dev/null
+++ b/packages/babel-plugin-transform-typescript/test/fixtures/namespace/clobber-class/input.mjs
@@ -0,0 +1,4 @@
+class A { }
+namespace A {
+  export const B = 1;
+}
diff --git a/packages/babel-plugin-transform-typescript/test/fixtures/namespace/clobber-class/output.mjs b/packages/babel-plugin-transform-typescript/test/fixtures/namespace/clobber-class/output.mjs
new file mode 100644
index 000000000000..98c88f006331
--- /dev/null
+++ b/packages/babel-plugin-transform-typescript/test/fixtures/namespace/clobber-class/output.mjs
@@ -0,0 +1,5 @@
+class A {}
+
+(function (_A) {
+  const B = _A.B = 1;
+})(A || (A = {}));
diff --git a/packages/babel-plugin-transform-typescript/test/fixtures/namespace/clobber-enum/input.mjs b/packages/babel-plugin-transform-typescript/test/fixtures/namespace/clobber-enum/input.mjs
new file mode 100644
index 000000000000..7b569657b080
--- /dev/null
+++ b/packages/babel-plugin-transform-typescript/test/fixtures/namespace/clobber-enum/input.mjs
@@ -0,0 +1,6 @@
+enum A {
+  C = 2,
+}
+namespace A {
+  export const B = 1;
+}
diff --git a/packages/babel-plugin-transform-typescript/test/fixtures/namespace/clobber-enum/output.mjs b/packages/babel-plugin-transform-typescript/test/fixtures/namespace/clobber-enum/output.mjs
new file mode 100644
index 000000000000..5a1aa715f308
--- /dev/null
+++ b/packages/babel-plugin-transform-typescript/test/fixtures/namespace/clobber-enum/output.mjs
@@ -0,0 +1,9 @@
+var A;
+
+(function (A) {
+  A[A["C"] = 2] = "C";
+})(A || (A = {}));
+
+(function (_A) {
+  const B = _A.B = 1;
+})(A || (A = {}));
diff --git a/packages/babel-plugin-transform-typescript/test/fixtures/namespace/clobber-export/input.mjs b/packages/babel-plugin-transform-typescript/test/fixtures/namespace/clobber-export/input.mjs
new file mode 100644
index 000000000000..8122f8e6cce5
--- /dev/null
+++ b/packages/babel-plugin-transform-typescript/test/fixtures/namespace/clobber-export/input.mjs
@@ -0,0 +1,3 @@
+export class N {}
+export namespace N {}
+export default N;
diff --git a/packages/babel-plugin-transform-typescript/test/fixtures/namespace/clobber-export/output.mjs b/packages/babel-plugin-transform-typescript/test/fixtures/namespace/clobber-export/output.mjs
new file mode 100644
index 000000000000..e7bc977078a7
--- /dev/null
+++ b/packages/babel-plugin-transform-typescript/test/fixtures/namespace/clobber-export/output.mjs
@@ -0,0 +1,5 @@
+export class N {}
+
+(function (_N) {})(N || (N = {}));
+
+export default N;
diff --git a/packages/babel-plugin-transform-typescript/test/fixtures/namespace/clobber-import/input.mjs b/packages/babel-plugin-transform-typescript/test/fixtures/namespace/clobber-import/input.mjs
new file mode 100644
index 000000000000..ef68acd5adb9
--- /dev/null
+++ b/packages/babel-plugin-transform-typescript/test/fixtures/namespace/clobber-import/input.mjs
@@ -0,0 +1,3 @@
+import N from 'n';
+
+namespace N {}
diff --git a/packages/babel-plugin-transform-typescript/test/fixtures/namespace/clobber-import/output.mjs b/packages/babel-plugin-transform-typescript/test/fixtures/namespace/clobber-import/output.mjs
new file mode 100644
index 000000000000..5ee84b002fe6
--- /dev/null
+++ b/packages/babel-plugin-transform-typescript/test/fixtures/namespace/clobber-import/output.mjs
@@ -0,0 +1,3 @@
+import N from 'n';
+
+(function (_N) {})(N || (N = {}));
diff --git a/packages/babel-plugin-transform-typescript/test/fixtures/namespace/contentious-names/input.mjs b/packages/babel-plugin-transform-typescript/test/fixtures/namespace/contentious-names/input.mjs
new file mode 100644
index 000000000000..efc42d05c9c9
--- /dev/null
+++ b/packages/babel-plugin-transform-typescript/test/fixtures/namespace/contentious-names/input.mjs
@@ -0,0 +1,36 @@
+namespace N {
+  namespace N {}
+  namespace constructor {}
+  namespace length {}
+  namespace concat {}
+  namespace copyWithin {}
+  namespace fill {}
+  namespace find {}
+  namespace findIndex {}
+  namespace lastIndexOf {}
+  namespace pop {}
+  namespace push {}
+  namespace reverse {}
+  namespace shift {}
+  namespace unshift {}
+  namespace slice {}
+  namespace sort {}
+  namespace splice {}
+  namespace includes {}
+  namespace indexOf {}
+  namespace join {}
+  namespace keys {}
+  namespace entries {}
+  namespace values {}
+  namespace forEach {}
+  namespace filter {}
+  namespace map {}
+  namespace every {}
+  namespace some {}
+  namespace reduce {}
+  namespace reduceRight {}
+  namespace toLocaleString {}
+  namespace toString {}
+  namespace flat {}
+  namespace flatMap {}
+}
diff --git a/packages/babel-plugin-transform-typescript/test/fixtures/namespace/contentious-names/output.mjs b/packages/babel-plugin-transform-typescript/test/fixtures/namespace/contentious-names/output.mjs
new file mode 100644
index 000000000000..749100aaa780
--- /dev/null
+++ b/packages/babel-plugin-transform-typescript/test/fixtures/namespace/contentious-names/output.mjs
@@ -0,0 +1,139 @@
+let N;
+
+(function (_N) {
+  let N;
+
+  (function (_N2) {})(N || (N = {}));
+
+  let constructor;
+
+  (function (_constructor) {})(constructor || (constructor = {}));
+
+  let length;
+
+  (function (_length) {})(length || (length = {}));
+
+  let concat;
+
+  (function (_concat) {})(concat || (concat = {}));
+
+  let copyWithin;
+
+  (function (_copyWithin) {})(copyWithin || (copyWithin = {}));
+
+  let fill;
+
+  (function (_fill) {})(fill || (fill = {}));
+
+  let find;
+
+  (function (_find) {})(find || (find = {}));
+
+  let findIndex;
+
+  (function (_findIndex) {})(findIndex || (findIndex = {}));
+
+  let lastIndexOf;
+
+  (function (_lastIndexOf) {})(lastIndexOf || (lastIndexOf = {}));
+
+  let pop;
+
+  (function (_pop) {})(pop || (pop = {}));
+
+  let push;
+
+  (function (_push) {})(push || (push = {}));
+
+  let reverse;
+
+  (function (_reverse) {})(reverse || (reverse = {}));
+
+  let shift;
+
+  (function (_shift) {})(shift || (shift = {}));
+
+  let unshift;
+
+  (function (_unshift) {})(unshift || (unshift = {}));
+
+  let slice;
+
+  (function (_slice) {})(slice || (slice = {}));
+
+  let sort;
+
+  (function (_sort) {})(sort || (sort = {}));
+
+  let splice;
+
+  (function (_splice) {})(splice || (splice = {}));
+
+  let includes;
+
+  (function (_includes) {})(includes || (includes = {}));
+
+  let indexOf;
+
+  (function (_indexOf) {})(indexOf || (indexOf = {}));
+
+  let join;
+
+  (function (_join) {})(join || (join = {}));
+
+  let keys;
+
+  (function (_keys) {})(keys || (keys = {}));
+
+  let entries;
+
+  (function (_entries) {})(entries || (entries = {}));
+
+  let values;
+
+  (function (_values) {})(values || (values = {}));
+
+  let forEach;
+
+  (function (_forEach) {})(forEach || (forEach = {}));
+
+  let filter;
+
+  (function (_filter) {})(filter || (filter = {}));
+
+  let map;
+
+  (function (_map) {})(map || (map = {}));
+
+  let every;
+
+  (function (_every) {})(every || (every = {}));
+
+  let some;
+
+  (function (_some) {})(some || (some = {}));
+
+  let reduce;
+
+  (function (_reduce) {})(reduce || (reduce = {}));
+
+  let reduceRight;
+
+  (function (_reduceRight) {})(reduceRight || (reduceRight = {}));
+
+  let toLocaleString;
+
+  (function (_toLocaleString) {})(toLocaleString || (toLocaleString = {}));
+
+  let toString;
+
+  (function (_toString) {})(toString || (toString = {}));
+
+  let flat;
+
+  (function (_flat) {})(flat || (flat = {}));
+
+  let flatMap;
+
+  (function (_flatMap) {})(flatMap || (flatMap = {}));
+})(N || (N = {}));
diff --git a/packages/babel-plugin-transform-typescript/test/fixtures/namespace/export/input.mjs b/packages/babel-plugin-transform-typescript/test/fixtures/namespace/export/input.mjs
new file mode 100644
index 000000000000..a27f292cbf1c
--- /dev/null
+++ b/packages/babel-plugin-transform-typescript/test/fixtures/namespace/export/input.mjs
@@ -0,0 +1 @@
+export namespace N {}
diff --git a/packages/babel-plugin-transform-typescript/test/fixtures/namespace/export/output.mjs b/packages/babel-plugin-transform-typescript/test/fixtures/namespace/export/output.mjs
new file mode 100644
index 000000000000..edd98b8f9582
--- /dev/null
+++ b/packages/babel-plugin-transform-typescript/test/fixtures/namespace/export/output.mjs
@@ -0,0 +1,3 @@
+export let N;
+
+(function (_N) {})(N || (N = {}));
diff --git a/packages/babel-plugin-transform-typescript/test/fixtures/namespace/fails/input.js b/packages/babel-plugin-transform-typescript/test/fixtures/namespace/fails/input.js
deleted file mode 100644
index 4db486e32f06..000000000000
--- a/packages/babel-plugin-transform-typescript/test/fixtures/namespace/fails/input.js
+++ /dev/null
@@ -1 +0,0 @@
-namespace N {}
\ No newline at end of file
diff --git a/packages/babel-plugin-transform-typescript/test/fixtures/namespace/fails/options.json b/packages/babel-plugin-transform-typescript/test/fixtures/namespace/fails/options.json
deleted file mode 100644
index 8449a74304e1..000000000000
--- a/packages/babel-plugin-transform-typescript/test/fixtures/namespace/fails/options.json
+++ /dev/null
@@ -1,3 +0,0 @@
-{
-  "throws": "Namespaces are not supported."
-}
diff --git a/packages/babel-plugin-transform-typescript/test/fixtures/namespace/multiple/input.mjs b/packages/babel-plugin-transform-typescript/test/fixtures/namespace/multiple/input.mjs
new file mode 100644
index 000000000000..35c080283606
--- /dev/null
+++ b/packages/babel-plugin-transform-typescript/test/fixtures/namespace/multiple/input.mjs
@@ -0,0 +1,2 @@
+namespace N {}
+namespace N {}
diff --git a/packages/babel-plugin-transform-typescript/test/fixtures/namespace/multiple/output.mjs b/packages/babel-plugin-transform-typescript/test/fixtures/namespace/multiple/output.mjs
new file mode 100644
index 000000000000..12b4c7a92253
--- /dev/null
+++ b/packages/babel-plugin-transform-typescript/test/fixtures/namespace/multiple/output.mjs
@@ -0,0 +1,5 @@
+let N;
+
+(function (_N) {})(N || (N = {}));
+
+(function (_N2) {})(N || (N = {}));
diff --git a/packages/babel-plugin-transform-typescript/test/fixtures/namespace/mutable-fail/input.mjs b/packages/babel-plugin-transform-typescript/test/fixtures/namespace/mutable-fail/input.mjs
new file mode 100644
index 000000000000..167274d7aee5
--- /dev/null
+++ b/packages/babel-plugin-transform-typescript/test/fixtures/namespace/mutable-fail/input.mjs
@@ -0,0 +1,3 @@
+namespace N {
+  export let V;
+}
diff --git a/packages/babel-plugin-transform-typescript/test/fixtures/namespace/mutable-fail/options.json b/packages/babel-plugin-transform-typescript/test/fixtures/namespace/mutable-fail/options.json
new file mode 100644
index 000000000000..1a58e10cc896
--- /dev/null
+++ b/packages/babel-plugin-transform-typescript/test/fixtures/namespace/mutable-fail/options.json
@@ -0,0 +1,3 @@
+{
+  "throws": "Namespaces exporting non-const are not supported by Babel. Change to const or see: https://babeljs.io/docs/en/babel-plugin-transform-typescript"
+}
diff --git a/packages/babel-plugin-transform-typescript/test/fixtures/namespace/namespace-flag/input.mjs b/packages/babel-plugin-transform-typescript/test/fixtures/namespace/namespace-flag/input.mjs
new file mode 100644
index 000000000000..fe71f4004e4a
--- /dev/null
+++ b/packages/babel-plugin-transform-typescript/test/fixtures/namespace/namespace-flag/input.mjs
@@ -0,0 +1 @@
+namespace N {}
diff --git a/packages/babel-plugin-transform-typescript/test/fixtures/namespace/namespace-flag/options.json b/packages/babel-plugin-transform-typescript/test/fixtures/namespace/namespace-flag/options.json
new file mode 100644
index 000000000000..186a430133f0
--- /dev/null
+++ b/packages/babel-plugin-transform-typescript/test/fixtures/namespace/namespace-flag/options.json
@@ -0,0 +1,4 @@
+{
+  "throws": "Namespace not marked type-only declare. Non-declarative namespaces are only supported experimentally in Babel. To enable and review caveats see: https://babeljs.io/docs/en/babel-plugin-transform-typescript",
+  "plugins": [["transform-typescript", { "allowNamespaces": false }]]
+}
diff --git a/packages/babel-plugin-transform-typescript/test/fixtures/namespace/nested/input.mjs b/packages/babel-plugin-transform-typescript/test/fixtures/namespace/nested/input.mjs
new file mode 100644
index 000000000000..87dd9140b28f
--- /dev/null
+++ b/packages/babel-plugin-transform-typescript/test/fixtures/namespace/nested/input.mjs
@@ -0,0 +1,26 @@
+class A { }
+namespace A {
+  export namespace C {
+    export class G {}
+    export const E = 7;
+  }
+  function M() {}
+  namespace M {
+    export const N = C.E;
+  }
+  export function D() {}
+  export namespace D {
+    const C = 5;
+    export enum H {
+      I = 11,
+      J = 13,
+      K = 17,
+    }
+  }
+  class F {}
+  namespace F {}
+  namespace G {}
+  enum L {
+    M = 19,
+  }
+}
diff --git a/packages/babel-plugin-transform-typescript/test/fixtures/namespace/nested/output.mjs b/packages/babel-plugin-transform-typescript/test/fixtures/namespace/nested/output.mjs
new file mode 100644
index 000000000000..1e85423d2c94
--- /dev/null
+++ b/packages/babel-plugin-transform-typescript/test/fixtures/namespace/nested/output.mjs
@@ -0,0 +1,49 @@
+class A {}
+
+(function (_A) {
+  let C;
+
+  (function (_C) {
+    class G {}
+
+    _C.G = G;
+    const E = _C.E = 7;
+  })(C || (C = _A.C || (_A.C = {})));
+
+  function M() {}
+
+  (function (_M) {
+    const N = _M.N = C.E;
+  })(M || (M = {}));
+
+  function D() {}
+
+  _A.D = D;
+
+  (function (_D) {
+    const C = 5;
+    let H;
+
+    (function (H) {
+      H[H["I"] = 11] = "I";
+      H[H["J"] = 13] = "J";
+      H[H["K"] = 17] = "K";
+    })(H || (H = {}));
+
+    _D.H = H;
+  })(D || (D = _A.D || (_A.D = {})));
+
+  class F {}
+
+  (function (_F) {})(F || (F = {}));
+
+  let G;
+
+  (function (_G) {})(G || (G = {}));
+
+  let L;
+
+  (function (L) {
+    L[L["M"] = 19] = "M";
+  })(L || (L = {}));
+})(A || (A = {}));
diff --git a/packages/babel-plugin-transform-typescript/test/fixtures/namespace/same-name/input.mjs b/packages/babel-plugin-transform-typescript/test/fixtures/namespace/same-name/input.mjs
new file mode 100644
index 000000000000..ff59e9d4fa36
--- /dev/null
+++ b/packages/babel-plugin-transform-typescript/test/fixtures/namespace/same-name/input.mjs
@@ -0,0 +1,12 @@
+namespace N {
+  namespace _N7 {}
+  export namespace N {
+    export function _N3() {}
+  }
+  export namespace N {
+    export class _N5 {}
+  }
+  export namespace N {
+    export enum _N {}
+  }
+}
diff --git a/packages/babel-plugin-transform-typescript/test/fixtures/namespace/same-name/output.mjs b/packages/babel-plugin-transform-typescript/test/fixtures/namespace/same-name/output.mjs
new file mode 100644
index 000000000000..b8db977b690f
--- /dev/null
+++ b/packages/babel-plugin-transform-typescript/test/fixtures/namespace/same-name/output.mjs
@@ -0,0 +1,29 @@
+let N;
+
+(function (_N2) {
+  let _N7;
+
+  (function (_N4) {})(_N7 || (_N7 = {}));
+
+  let N;
+
+  (function (_N6) {
+    function _N3() {}
+
+    _N6._N3 = _N3;
+  })(N || (N = _N2.N || (_N2.N = {})));
+
+  (function (_N8) {
+    class _N5 {}
+
+    _N8._N5 = _N5;
+  })(N || (N = _N2.N || (_N2.N = {})));
+
+  (function (_N9) {
+    let _N;
+
+    (function (_N) {})(_N || (_N = {}));
+
+    _N9._N = _N;
+  })(N || (N = _N2.N || (_N2.N = {})));
+})(N || (N = {}));
diff --git a/packages/babel-plugin-transform-typescript/test/fixtures/namespace/undeclared/input.mjs b/packages/babel-plugin-transform-typescript/test/fixtures/namespace/undeclared/input.mjs
new file mode 100644
index 000000000000..fe71f4004e4a
--- /dev/null
+++ b/packages/babel-plugin-transform-typescript/test/fixtures/namespace/undeclared/input.mjs
@@ -0,0 +1 @@
+namespace N {}
diff --git a/packages/babel-plugin-transform-typescript/test/fixtures/namespace/undeclared/output.mjs b/packages/babel-plugin-transform-typescript/test/fixtures/namespace/undeclared/output.mjs
new file mode 100644
index 000000000000..eca9b4570a75
--- /dev/null
+++ b/packages/babel-plugin-transform-typescript/test/fixtures/namespace/undeclared/output.mjs
@@ -0,0 +1,3 @@
+let N;
+
+(function (_N) {})(N || (N = {}));
diff --git a/packages/babel-plugin-transform-typescript/test/fixtures/options.json b/packages/babel-plugin-transform-typescript/test/fixtures/options.json
index 5c79172a6082..ed634a8c9790 100644
--- a/packages/babel-plugin-transform-typescript/test/fixtures/options.json
+++ b/packages/babel-plugin-transform-typescript/test/fixtures/options.json
@@ -1,3 +1,3 @@
 {
-  "plugins": ["transform-typescript"]
+  "plugins": [["transform-typescript", { "allowNamespaces": true }]]
 }
diff --git a/packages/babel-types/src/definitions/typescript.js b/packages/babel-types/src/definitions/typescript.js
index f6a89fa8dcd3..843f2408ecc9 100644
--- a/packages/babel-types/src/definitions/typescript.js
+++ b/packages/babel-types/src/definitions/typescript.js
@@ -399,6 +399,7 @@ defineType("TSModuleDeclaration", {
 });
 
 defineType("TSModuleBlock", {
+  aliases: ["Scopable", "Block", "BlockParent"],
   visitor: ["body"],
   fields: {
     body: validateArrayOfType("Statement"),
diff --git a/packages/babel-types/src/validators/generated/index.js b/packages/babel-types/src/validators/generated/index.js
index 890999e5d0e1..076495d5cb28 100644
--- a/packages/babel-types/src/validators/generated/index.js
+++ b/packages/babel-types/src/validators/generated/index.js
@@ -3350,6 +3350,7 @@ export function isScopable(node: ?Object, opts?: Object): boolean {
     "ForOfStatement" === nodeType ||
     "ClassMethod" === nodeType ||
     "ClassPrivateMethod" === nodeType ||
+    "TSModuleBlock" === nodeType ||
     (nodeType === "Placeholder" && "BlockStatement" === node.expectedNode)
   ) {
     if (typeof opts === "undefined") {
@@ -3382,6 +3383,7 @@ export function isBlockParent(node: ?Object, opts?: Object): boolean {
     "ForOfStatement" === nodeType ||
     "ClassMethod" === nodeType ||
     "ClassPrivateMethod" === nodeType ||
+    "TSModuleBlock" === nodeType ||
     (nodeType === "Placeholder" && "BlockStatement" === node.expectedNode)
   ) {
     if (typeof opts === "undefined") {
@@ -3401,6 +3403,7 @@ export function isBlock(node: ?Object, opts?: Object): boolean {
     nodeType === "Block" ||
     "BlockStatement" === nodeType ||
     "Program" === nodeType ||
+    "TSModuleBlock" === nodeType ||
     (nodeType === "Placeholder" && "BlockStatement" === node.expectedNode)
   ) {
     if (typeof opts === "undefined") {