Officials in China appear to have launched a crackdown on the encrypted messaging service WhatsApp.
Some users attempting to set up a new WhatsApp account have been greeted with error messages, while others have had difficulties sending images and videos.
Censorship controls on social media are being tightened ahead of the Communist Party congress next month, where President Xi Jinping is due to be appointed to a second five-year term.
Facebook-owned WhatsApp is popular in China because it offers users more privacy than the country’s own messaging apps, which are monitored by the government.
However, even Chinese-run technology companies can fall afoul of Beijing’s strict rules, with three web giants receiving “maximum penalties” for failing to remove illegal online content.
The online forum Tieba, micro-blogging site Weibo and the messaging app WeChat have been accused by a watchdog of allowing the publication of pornographic and violent material – as well as other types of banned content.
The Cyberspace Administration of China also said the companies had failed to block material that “promoted ethnic hatred”.
Since 2000, websites in China have been responsible for ensuring any information posted on their platforms is legal.
Further restrictions on permissible content were brought into force this year, and tech companies are now required to store user data inside the country.
Foreign networks such as Twitter, Pinterest and Facebook – as well as dozens of overseas media websites – have been blocked in China for years.
(c) Sky News 2017: WhatsApp disruption in China as censorship controls tightened