24hour visa For Transit not direct checked through

Tam, your itinerary is definitely eligible for 24 hour visa free transit and you do not need any kind of visa. It is important to emphasize that you are definitely allowed to travel on separate tickets and on unrelated airlines and also to perform a self-transfer in Chengdu.

So, during your check-in in London, you will just declare that you are traveling to HCMC via Chengdu (China) using 24 hour visa free transit and you will present your ticket from Chengdu to HCMC. Shortly after you will be allowed to board the plane.

Upon landing in Chengdu, the first thing you will do is to approach 24/144 hour visa free transit counter where you will apply for a temporary entry permit because you will have to enter China formally in order to perform new check-in. Just be relaxed because 4 hours are enough to perform all the formalities. At the moment of application you will present your flight ticket to HCMC. This application is free of charge and your permit will be granted to you. When the permit is granted, you will head to the immigration and then to perform the formalities for your check-in for a flight to HCMC.

Basically, this is all and there will be no problems for you whatsoever. Have a nice journey.