I do believe that majority of mining farm is located in China but I doubt that majority of it is owned by chinese. The reason for this is that if ever the majority of hashes is owned by Chinese then the increase in blocksize will never had problem in getting the percentage it wanted for hardforking bitcoin. But it seems it isn't controlled by chinese.
Have you heard of bitmain it is one of the largest bitcoin mining farm in the world and it is owned by the Chinese. Though there are other mining farms that are not owned by the Chinese and was only set-up in that country due to cheap electricity and cheap manpower cost. But reagrdless of it being owned by Chinese or by foreign entities we cannot deny the fact that it is located withing the political boundaries of China and can be regulated by the Government of China. If the Chinese government will make a strict policy on the release of bitcoins into the market then that is the time when they will gain control.
The moment the government of China will make a move to control bitcoin as in restricting transactions or blocking transfers from certain addresses...nothing will happen.
Other miners will pick those transactions and nothing will happen.
What can they do?
Force double spending? Killing a business that bring money inside China?
Trying to control it won't work trying to kill it is hilarious so...in the end.
Nobody gives a damn about China.