30 hour China Layover

Zoe, since your layover is 30 hours long, you will not use 24 hour visa free transit, but 144 hour visa free transit. Please, just use correct terminology because this is not a visa, but visa free transit, so there is no visa of any kind.

It is important that your flight itinerary is:

London - one Chinese city - Hanoi

You are allowed to have just one mainland Chinese stop, so have that in mind. When flying on 144 hour visa free transit you cannot have two mainland Chinese stops in a row.

When you land in a Chinese city, 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 by presenting your flight itinerary and your accommodation booking. After a short check, you will be granted a permit and you will exit the airport to enjoy your time on your own. This application is free of any charge.

Just to conclude, if you have just one stop within mainland China, you will be covered by 144 hour visa free transit and you do not any kind of visa. Have a nice journey.