We were hoping to get the train from hanoi in Vietnam to Hong kong.

Hi, Louise, how long is your first stay in mainland China? If the time is not more than 24 hours, the single entry will suffice for your travel. Keep in mind that the 24 hours count from the midnight after your arrival, so that you acctually enjoy a longer allowed stay duration. If you need to stay longer for the first visit, then you should get a double entry one. An alternative choice for you is to enter China with the singe entry, and then apply for another one at Hong Kong.

Our plan is to get the train from hanoi at 20:40 to Nanning arriving at 10:10 next day. Then travelling from Nanning East at 13:30 arriving in ghanzou at 17:40. We then get the 20:40 train to Hang hum which arrives at 22:40.

At what point do they check passports to stamp in and out? This trip takes 25 hours. Do you know if China trains are subject to delays as this would become a problem? If this is not realistic, are we able to buy another single entry one instead of voiding our current one to buy a double entry one?

Louise, they will check your passport at the entry point and exit point, which are respectively Nanning and Guangzhou I guess. As the 24 hours defined by the 24-hour direct transit policy start from the midnight after your arrival, so I think your layover does not exceed the 24 hours. In addition, it’s possible that trains are subject to delays. If the delay results in your layover exceeding 24 hours, you can go to the local exit and entry office to apply for a VOA. I personally think you don’t need to buy a double entry one.