I don't know about 'citation', but when I crossed from Hong Kong to Shenzhen last month I had to exit Hong Kong's immigration and enter China's and vice-versa on the way back.
It's substantially easier to visit Hong Kong than China (visa at the airport vs. visa in your home country before you travel), unless you have an APEC card of course
It's substantially easier to visit Hong Kong than China (visa at the airport vs. visa in your home country before you travel), unless you have an APEC card of course