Wherever there is an interruption in service due to censorship, the Internet traffic will just route around the unaccessible site. This was the original intention of the Internet when created by DARPA (Defence Advanced Research Projects Administration.) The purpose was that if the Soviet Union would attack the United States they could blow holes in the network, but the traffic would route itself around the broken bits of Internet.
In China, there are central servers (Internet Service Providers) that through which all of the Internet access for the country flows. These specialised servers are called firewalls. This is the simplest way to block access to web-site that Beijing feels are subversive; however, users are still able to access the Internet by making long distance calls to Internet service providers in neighbouring countries.