Access to the Gmail website has been blocked for some time in China, but now the Chinese government is also blocking access to Gmail through apps. The block affects not just the official Gmail apps, but also accessing Gmail through third-party apps.
Said Google in a statement:
"We've checked and there's nothing wrong on our end."
Traffic to Gmail from China, according to Google's Transparency Report has plummeted to next to nothing, indicating that there are still some Chinese users that have managed to circumvent the block by using a VPN, but most are currently out of luck. Gmail joins Google Search and Google Maps in being blocked by Chinese authorities, as well as Facebook.