Right now, it's unclear. With the launch of the iPhone Air, Chinese carriers are supposed to support eSIM but it is delayed. eSIM would still require the same real name verification that physical SIMs do, so it would not be as easy as buying one from an online vendor.
I am not specifically sure about 3HK, but other Chinese carriers like China Mobile have no citizenship requirements for getting a number, simply being a tourist will suffice. Though you might need a visa instead of TWOV.