I live in HK; unfortunately not the same laws as China so I can't comment on knives being shipped in but I know swords cannot be shipped into China.
If you're selling a large fixed blade, you might fall foul of customs based on the sword laws. I honestly don't know about folders or small fixed blades being shipped in but I understand from a local friend that it is ok, though take that with the guarantees it comes with.
There is a member here, Stormcrow, I believe, who has posted some short swords in this forums sword discussion area. He has sent some machete style blades to China so maybe worth contacting him. Not sure if he sent them to HK or China direct.
FYI, shipping most knives and swords to HK is perfectly legal and I've heard that people will have items delivered and held at a HK address until they can be picked up by hand and carried across the border. That's not to break the law as such, more that the definition of sword/knife can be vague at best with the customs so folk prefer to deal face to face with the item in hand - if stopped.