Could be an option if you take the fast train in hong kong to guangzhou?

Dear, you mean you want to enjoy the 72 hour free transit in Guangzhou? If yes, you cannot enter Guangzhou by train, and after staying in Guangzhou for less than 72 hours, you need to fly to a third country or region. If you travel like HK-Guangzhou-a third country and travel by flights all the way, you will be eligible for the 72 hour free transit in Guangzhou.