I guess it one of those panic sales, it happens from time to time, and it is nothing to worry about. Price of bitcoin always fluctuate, it is going up and down and up and down again, it is always like that. Unless you are new to bitcoin and do not know this things. I have also heard that China banned local bitcoin exchanges, and i think that is not truth. Most powerful miners are from china, and it won't be that easy to stop them.