Gmail is the most popular email service in the world. In February 2016, Google announced that Gmail had passed 1 billion active users, and with their growth rate, they must be at 1.3 billion today. So the chances that someone travelling to China is actually using Gmail, is quite high.
The problem started in 2010 when Google decided to close their Chinese office. They did that after refusing to cooperate with the Chinese government who asked access to the accounts of users who access Gmail from China.
Since then, Gmail is blocked in China. Not always, but most of the time.
There are several ways to access websites, same way like many users use to access Facebook, by simply using Proxy services, VPNs, or TOR.
It all depends on what exactly you need.
If you are an engineer, with tons of technical knowledge, who knows how to configure routers, install services, and know what to do and most importantly what not to do, checkout TOR. It is free and it is working. However, as mentioned here, it is complicated.
The second option, is to use a web based proxy. The advantage is that you do not need to install anything, just open your browser and you’re done. You need to make sure that this proxy works in https ad that https is not broken.
The last option, which is not a bad one, is VPN. The thing is you’ll need to install it in advance, preferably before you left your home country. Installing a VPN while you are in China is a bad idea. The chances that you will install a Chinese virus pretending to be a VPN service are too high 🙂
In any case, just make sure not to do anything stupid 🙂