A quick question. I have a double entry 2x60 days visa in PRC. Do I need to leave to and reenter into China to use the second entry, or can I stay for the full 120 days without leaving any time before?
The key word is double "entry". Yes you have to leave. A 60 day visa allows you to stay in the country for a maximum of 60 days, then you have to leave. This is pretty much the rule anywhere in the world. On the brightside, a trip to Hong Kong or Macau counts as leaving.