The encrypted messaging app Signal, recommended by Tesla's Elon Musk, appeared to have been blocked in China on Tuesday, closing off one of the last US social media platforms still freely available in the country.
Users of the free app, which has surged in popularity globally after rising privacy concerns, were unable to access it without a virtual private network (VPN).
China has deployed a vast and sophisticated system to scrub the internet of dissent and prevent citizens from accessing international social networking platforms such as Facebook and Twitter, in what is known as the "Great Firewall".
Signal's website has been banned since at least March 15, according to the GreatFire.org website which tracks online censorship in China, although the app remains available on China's App Store.
