Chinese Internet authorities have opened cases to investigate three social media platforms -- Tencent's Wechat, Sina Weibo and Baidu Tieba, for not stopping the circulation of illegal online content, the Cyberspace Administration of China (CAC) said Friday.

The administration has received reports from users that illegal content, including pornographic, violent, terrorist and fake information, was being spread on the three platforms, according to a statement published on CAC website.

The illegal content is harmful to national security, public security and social order, the CAC said.

The companies are suspected of violating the country's cyber security law, as they failed to stop the information being published and spread on their platforms, a CAC official said.

China's Twitter-like Sina Weibo, the instant messaging app WeChat, and Baidu Tieba, the popular bulletin board consisting of 19 million sub-forums, are considered the three largest communication platforms in China.