Different entry/departure cities in China

Hello, my questions is regarding the fact that we have some kind of proof of being accommodated in China in order to get a visa. My friend and I already booked the first night in Beijing but no other night. As we have our tickets mentioning the fact we leave from HKG, do we also have to have a proof of any accommodation there? We don't plan too many things before making it to China.
Do the Chinese authorities need more proof of accommodation during our stay or is the fist night enough?