Module elasticsearch not found within Angular2 (AngularCLI)

I try to use the Elasticsearch NPM Module in my Angular2 App.

I import it within my service using:

import { Client, SearchResponse } from 'elasticsearch';

Typescript Compiler does not complain, but ng serve outputs:

Cannot find module 'elasticsearch'

Same happens if I try to use:

import { Client, SearchResponse } from '../../node_modules/elasticsearch/webpack_config/angular.js';