It's a different process and it's harder. As I understand it, the Chinese employee will also need permission from various people in the mainland to work abroad. Exactly how hard this is depends on many factors, including whether s/he is living in their "home" town - if not s/he may have to travel there to sort out some bureaucracy.
I would budget 4-6 months to make it all come together (although it may happen a bit quicker than that).
Start here for the Hong Kong part:
http://www.immd.gov.hk/ehtml/hkvisas_3.5.htm
