error TS2687: All declarations of 'observable' must have identical modifiers

Had the same issue after updating @types/node to 10.3.0. After downgrading to version 10.1.4 everything is working again. I think rxjs has to be updated to work with the newest @types/node version. So at the moment, just use the older version:

npm install @types/[email protected]

UPDATE: The fix on RxJS is already done -> https://github.com/ReactiveX/rxjs/pull/3773 . Now they just have to merge the changes and publish the new version.