Hong Kong and China, 'One Country, two Systems' or when it comes to visas and immigration just two systems. Hong Kong and China have two completely different immigration systems and access to one does not grant access to the other. It can trip even an experience traveller up.
There are also other differences, from the currency to the practicalities of the Great Chinese Firewall. If you're planning to visit Hong Kong and China in the same trip read our guide to Hong Kong and China - what you need to know for tips and hints on some of the most common problems.