Back when I got in 2016 China would regularly manipulate the price of bitcoin via positive/negative announcements regarding it's legality. They eventually shut down Chinese exchanges in 2017-18, thus eliminating their influence over it's price and driving bitcoin onto the black market where it does it's work best.
Bitcoin mining is concentrated in China more-so than other places for two non-threatening reasons, 1) subsidized electricity 2) The ASIC manufacturer's are in China. ASIC stands for application specific integrated circuit, basically a highly specialized chip who's architecture can only run a single application, in cryptocurrencies case it's the mining algorithms like SHA256 for bitcoin. Keeping up with the latest hardware is the name of the game in this highly competitive business, China just happens to have an advantage here specifically in "first dibs" to ASICs.
Some of the smaller cryptocurrencies, like the ones mined on graphics cards for example are vulnerable to 51% attacks. That's where most of the network is taken over by nodes that will validate invalid transactions. The hashing power alone behind bitcoin would require a massive (realistically unaffordable) coordinated effort to achieve. Most people there mine bitcoin semi illegally. China has several more legit large scale mining organizations as well, but realistically coordinating all of them to execute a 51% on the network (even if they were willing/able to) is technically unfeasible.
