Thailand - Guilin - Hong Kong

You are allowed to do that in principle, but there are some details you should be aware of.

1) 72 hour visa free transit allows you in reality a bit more time that you have mentioned because it is: day of arrival + 72 hours. In other words, if your flights are convenient, you can arrive in the morning of your arrival day and the 72 hour clock starts ticking at the beginning of the following day
2) The greatest problem for your itinerary, that is theoretically ideal, is the fact, at least as far as I know, that there are no direct flights from Guilin to Hanoi and vice versa and that makes your entire plan impossible to perform. You can maybe replace Hanoi with Taipei:

HK - Guilin - Taipei - Guilin - Thailand

Sam, I have to correct myself because 72 hour visa free transit in Guilin starts exactly at the moment of your arrival and not from the next day of your arrival. Having this in mind, you have to reprogram your schedule to fit the mentioned rule in Guilin in the same way as you have to do with your flights.

Hi,

Are you sure about this? I have seen on various websites:

"The 72-hour limit is calculated starting from 00:00 the day after arrival. For example, if a traveler arrives at Guilin Liangjiang Airport on August 1, 2019, the visa exemption period is calculated starting from 00:00 on August 2, 2019. The traveler must leave Guiiln Liangjiang Airport before 23:59 on August 4, 2019 on an international flight."

Is there an official Chinese website that tells you 100%? As obviously I don't want to accidentally break the visa rule, or get stuck/miss flight etc.

I was confident that Guilin 72 hour visa free transit starts in the way as you have mentioned. Anyway, just a day ago one of great contributors to this website, under the user name "John Doe" has mentioned that this logic as you have explained above is not valid for Guilin and Harbin. To be honest, I respect his knowledge and that is the reason why I have written my additional post. Anyway, it is true as you say that there are no confirmations that John Doe was right. In any case, I would suggest you to call Guilin Frontier Inspection Station: +86-0773-3603750. I know, the calls to China could be expensive, but in my opinion, you will get a first hand official information. I apologize for any inconvenience, but I just wanted to offer you the best available information.

Thanks thats a helpful response, I will contact them - as I am in Macau already maybe the phone charge won't be excessive