The volume can easily be explained by the fact that the chinese exchanges have no trading fees. As an example some Chinese traders may be selling during the rally to buy back a few minutes later at a little lower price, which isn't as easy if there are trading fees that will cut into profit.
That may indeed happen, but it does not explain why they kept trading vigorously while the price was nearly stable, varying by only 2-3 yuan in each minute. Why wasn't this volume an hour ago, when price was varying by the same amount?