hi

Anthony, if your entire transit time in Guangzhou is less than 24 hours, you are definitely eligible for 24 hour visa free transit and you don't need any kind of visa.

You will print out your flight tickets and have those printouts with you. Also, you will declare at check-in in Bangkok that you will travel to Christchurch via Guangzhou using 24 hour visa free transit. After a short check of your tickets, you will be allowed to board the plane. During your check-in, you will inform yourself whether your luggage will be tagged all the way to Christchurch. I assume that this will be a case, especially if you are traveling by China Southern. Anyway, you should ask, just for a case.

Upon your arrival in Guangzhou, you will clear the necessary formalities and after that, you will just proceed to your boarding gate for your onward flight to Christchurch.