Mainland China users of the US audio app Clubhouse said they were experiencing internet access disruptions, stoking concerns it had been blocked by China's so-called Great Firewall.
Users of China's Twitter-like social media app Weibo began posting that they were having issues accessing the Clubhouse app at around 7:30 pm local time (1130 GMT).
Some posted screenshots of a message the app displayed when they tried to open it, which said "an SSL error has occurred and a secure connection to the server cannot be made."
The Clubhouse app had in recent days attracted masses of new users from mainland China, who took part in discussions on rights, national identity and other sensitive topics.
Clubhouse did not immediately respond to an emailed request for comment. The Cyberspace Administration of China, the country's top internet regulator, did not respond to phonecalls made outside its office hours.
"Clubhouse has been walled" said one Weibo user, referring to the system China uses to regulate its internet that blocks many Western social media apps such as Facebook and Twitter.