Visting Hong Kong but flying back from Guangzhou

Hello, we are visiting Hong Kong for few days, but our return flight departs from Guangzhou (there were no seats available on Qatar Airways from Hong Kong at all, so we had to book from Guanzhou).
Do we need the chinese visa, or can we enjoy the 24 hour direct transit if we take from Hong Kong the train to Guangzhou and than taxi directly to the airport, we would stay in China just for few hours.

Thank you very much!

best regards,
Zbigniew