People from Mainland China need a special permit to enter Hong Kong. I don't think anyone doubts Hong Kong is part of the PRC by now. The fact that there are border and immigration controls within China isn't something new. Of course with an independent government and military Taiwan is de-facto independent, but having to get a "visa" to visit Taiwan doesn't really mean much.

https://en.wikipedia.org/wiki/Exit-Entry_Permit_for_Travelli...