China in my opinion can control bitcoin's price, since if all their miners sell at the same time, it would cause a very big dump on bitcoin's price. For now, I think those miners are independent and not controlled by the government. Hope that China won't plan to control bitcoin's price just yet. If they do, they will just need to order their miners and bitcoin users to sell all of their bitcoins at the same time or by banning bitcoin causing the miners to sell at the same time
Metaphorically speaking, we have already been there
The Chinese authorities have already effectively banned Bitcoin from trading in China. Now we see runaway prices going straight to the moon. Even if they make the Chinese miners sell all their stashed bitcoins somehow (provided there are any in the first place), that could only make the prices crash momentarily, and we will see buying wall rising to the sky covering the sun itself. Obviously, the Chinese government is not so much interested in controlling Bitcoin prices as driving Bitcoin out of the country altogether