WhatsApp faced at least a partial block in China after a censorship crackdown by the government, as users took to other social media platforms including Twitter to report outages.

At one point WhatsApp users could send text, but not images.

Apparently, the government increased social media censorship in the run-up to the 19th Communist Party Congress, which is considered a politically sensitive event.

The news comes just days after University of Toronto’s Citizen Lab said the scope of censorship of keywords and images on WeChat and Sina Weibo, China’s version of Twitter, related to Liu Xiaobo, a Nobel Peace Prize laureate and a political prisoner who recently died in government custody, expanded greatly.

“Concerned that martyrdom around Liu may spur collective action, as well as being concerned about saving face, the knee-jerk reaction of China’s authorities is to quash all public discussion of Liu, which in today’s world translates into censorship on social media,” wrote Ronald Deibert, director of Citizen Lab.

In China, WhatsApp is not as popular as Tencent’s WeChat, but is preferred by some because it is thought to be less closely monitored.

While WhatsApp messages are encrypted, WeChat is unencrypted and highly censored.

In December 2016 it was reported WeChat censors messages containing certain key words relating to social issues and politics, even when users travel outside of the country.

Some users have been using virtual private networks to get around the block, but China’s government initiated a crack down on them too.

These tools are often used in the country to circumvent China’s censorship apparatus, known unofficially as The Great Firewall.

In Brazil, WhatsApp has been blocked on several occasions after the app maker failed to submit messages which could potentially help the court in a drugs case.