I´ve been there many times. Actually too many.
In HK you´ll find policemen carrying SW revolvers, HK MP5 SMG and even Security Guards carry good stuff there. And you feel safe in HK, be sure.
In China cops aren´t ussually armed. Those who are carry semi autos chambered in somewhat .32 ACP size rounds. Dont´t know the round they use but it´s stopping power is... guess.
There are also many SMG chambered in the same tiny round but you´ll only find them in airports, police stations and so on.
The only place where I found real stuff, I mean AK´s in 7.62x39, machine guns, anti aircraft guns and much more, was in a military-industrial area in the South of Beijing. It was three years ago.
Anyway it´s not easy to see a gun in China. Better this way.