Typescript can't import files without extension

I am trying to import files in my new Angular2 project. The entry file "main.ts" is able to import an other typescript file using:

import { AppModule }              from './module/app.module';

"app.module.ts" on the other hand is not able to import a ts file without a file extension:

import { AppComponent }             from '../component/app.component';

If I add ".ts" to the file name everything works as expected...

What is my mistake? I assume I am doing everything as per angular guide (https://angular.io/docs/ts/latest/guide/webpack.html)

I have node 6.9.4, npm 4.2.0, typescript 2.3.2, Angular 4.1.0 and Webpack 2.5.1 installed

via donnikitos