Chinese internet giants Tencent, Baidu and Sina Weibo are under investigation for cyber-security violations, the mainland's office for cyberspace administration said on Friday.
An English translation of a notice on the office's website said the social media platforms of the three companies — WeChat, Tieba and Weibo respectively — have users spreading "violence and terror, false rumors, obscene pornography and other content that endangers national security, public safety and social order."
Citing earlier investigations, the notice said the platforms were "suspected of violating cyber-security laws and did not fulfill duties to manage information published by their users."
Tencent shares in Hong Kong were in the red following the news. The stock was down more than 2 percent following earlier losses of around 4 percent.
Baidu and Sina trade in New York and investors will be watching for any reaction at the U.S. market open.
CNBC's Barry Huang contributed to this report.