To take control of bitcoin, you need to take control of 80% if not all the networks and even at that moment, you'd still need a lot of power and money (for the equipment) to be able to pull it off and China's lacking in money already if you're keeping up with the Chinese stuff that's reported by investigative reporters so I don't believe that it's in their agenda to take over the bitcoin network anytime soon, pretty sure that whatever they're doing now, bitcoin or any cryptocurrency has no relation to it or anything like that.
Why would they need 80% and not just 51%?
China has no problem finding the money to build large scale infrastructure projects. I don't see how it wouldn't be possible for them to get 2-3 billion dollars worth of ASIC miners. Also with the current block reward it would only require 32mil USD a day worth of power to produce majority of the hash power. Based on my rough math this would require a 12GW power source and china has a large number of power plants to spread that over. For reference Chinas largest power plant is Three Gorges Dam with 22GW.