TAIPEI—Messaging app Signal became unusable for many people in mainland China this week, stifling one of the last widely used messaging apps that could send and receive encrypted messages in the country without a virtual private network.
The government’s apparent move to block Signal intensifies its hold on public and private discourse in China, where many social-media and messaging apps, including Facebook , Twitter and, most recently, the popular social-audio platform Clubhouse, have been banned.
Signal users in mainland China started reporting around Monday evening problems with sending and receiving messages in the app. Using a virtual private network, or VPN, a tool that enables internet users to circumvent China’s elaborate system of web filters, resolved those issues, which led users to conclude that the app had been blocked in China.
Some also reported problems with registration, another common censorship practice that affected Clubhouse last month, where users aren’t able to sign up with their phone numbers because the verification text code is never received.
The problems began on Sunday and included halted registration and network blocks, a person familiar with the matter said. The Cyberspace Administration of China, the country’s internet regulator, didn’t immediately respond to a request for comment.