Clubhouse, the popular audio-chat social networking app, has become a surprise hit among mainland Chinese users, according to a report in the South China Morning Post. But with users across social media platform Weibo complaining about not being able to access the app, it seems to have been blocked.

In China, it’s rare for foreign social media to gain traction. Not only are foreign apps and sites like Google, Facebook, Instagram and Twitter blocked by the country’s “great firewall” but domestic developers have also flourished, creating social media products that specifically cater to the needs of Chinese netizens - such as WeChat, Weibo and Douyin (the Chinese pre-cursor to TikTok).

This made the sudden success of Clubhouse a surprise. Though the app is not available on China’s Apple App Store and is invite only, mainland-based internet users have been gaining access in increasing numbers by using overseas Apple IDs and buying invitation codes from e-commerce platforms like Alibaba’s Taobao, where a search for “Clubhouse invitation” brings up invitation codes (which are normally free) for sale for as much as 329 yuan ($50). At present, it remains unclear whether the app has been blocked or is simply temporarily unavailble to users in the mainland.

Clubhouse is seen as an uncensored platform for social and political discussion, which is stifled on the Chinese internet by a comprehensive censorship regime. But it’s far easier to block key words en masse on a text-based platform, than to block controversial topics discussed via audio files on Clubhouse.

Indeed, topics being discussed in Clubhouse chats relating to Hong Kong’s protest movement, Taiwan and the detention of ethnic Uighurs in the northwestern region of Xinjiang would quickly be quashed on domestic Chinese social media sites.

Even among those using the app, there is a widely-held belief that Clubhouse has a short shelf life as a platform for free expression in China, with its increasing popularity likely to lead to scrutiny from Chinese authorities.

“I’ve finally tried Clubhouse … and my biggest impression: it’s such a miracle that it’s still accessible in mainland China,” wrote Zhang Taisu, a professor at Yale Law School in a Weibo post on Sunday.