Back in June 2014, a large number of Google services came under attack by the Great Firewall of China. This was prior to the anniversary of the Tiananmen incident, and was done by disruption of connections to all Google IP addresses. These attacks continued over the year to the point where the web interface of GMail was unaccessible in China. Only IMAP, SMTP, and POP3 were accessible.
This has just changed, as starting from the 26th of December even more of GMails IP addresses were blocked by the Great Firewall of China. From Google’s own Transparency Report, you’ll see a massive dropoff of Chinese traffic.
It seems as though China has launched a large campaign against foreign online services in the past year, possibly to establish complete control over the Internet in China. If you are in, or heading to China, we highly recommend obtaining a VPN if you need to access the rest of the Web.