I have been looking for multiple sources of information on this,
the problem is that what you see as "sources" are mostly poorly researched and written articles by news sites or individuals that seek to be heard.
and most seem to agree that at least 40% and up to 65% of the mining hash-power is coming from China.
What prevents their government from attempting a hostile take over of the farms?
there is a difference between a mining farm and a mining pool. there are Chinese owned mining pools that have servers in multiple places and the miners connecting to these pools (multiple) count for as much hashrate as 65%.
then there are mining farms that are among those miners that connect to those pools that could only have 1% of hashrate or less.
taking over a pool means miners abandon that pool and connect to another server.
taking over a mining farm means taking over a small percentage of hashrate.
After looking at what Justin Sun has done with the Steem Blockchain (I know its dPoS vs PoW)
apart from the difference in algorithms, another problem was that steem was already centralized which is why he could do what he did. in comparison bitcoin (both hashrate and nodes) are decentralized and distributed all over the world. so there is no single point of attack, for example as i said above you'll have to take over thousands of miners to gain a meaningful amount of hashrate that could be used for an attack. and if such actions were noticed a hard fork could prevent such attacks.
of course a better "prevention" mechanism is always more decentralization meaning more distributed hashrate, more number of mining pools coming from different parts of the world, more bitcoin full nodes coming from all parts of the world.