Yes, in your case, if you move to Hong Kong by rail, you need to issue an individual Chinese visa, and not just a visa, but a two-fold Chinese visa if you plan to return from Hong Kong to Guangzhou .The fact is that according to the rules of the 72-hour visa-free transit both arrival and departure to / from China should be from one port .So, if you were flying from Guangzhou to Hong Kong and vice versa, you could take a visa-free stay in Guangzhou on the way back (on the way there you would have to transit without passing the passport and customs control at the Guangzhou airport).If you say that you have even more weeks before departure, you still have time to issue an individual Chinese visa, or book flights from Guangzhou to Hong Kong - Guangzhou (only do not forget when you register for flight from Hong Kong to warn airline representatives that you intend to request upon arrival at Guangzhou 72-hour visa-free transit) .