China appears to be blocking all access to Wikipedia after previously only censoring the Chinese-language editions of the online encyclopedia.

The blocking started last month, according to an internet monitoring service operated by the Tor Project. Attempting to access any Wikipedia page from within the country, no matter the language, will now trigger a connection error.

A separate censorship monitoring group, Greatfire.org, says China has blocked access to Wikipedia since April 22. Local users on Chinese social media platforms say they've also been "walled" from the site.

It's unclear why the Chinese government has blocked the sites. But observers speculate it may be related to the upcoming 30th anniversary of the Tiananmen Square massacre, which occurred on June 4, 1989. The country's government has generally banned all discussion of the event, which resulted in the Chinese authorities using military force to squash a pro-democracy movement led by students.

It's possible the blocking may only be temporary. In January, China mysteriously blocked and then ublocked Microsoft's Bing search engine.

Over the years, the country has selectively blocked certain pages on Wikipedia that have been critical of its Communist-led government. However, in 2015, China began blocking all access to the Mandarin-language pages of Wikipedia after the encyclopedia site moved to HTTPS encryption by default in order to protect users from unwarranted surveillance.

So far, the Wikimedia Foundation hasn't commented on the blocking. To access a censored website from within China, users can install a VPN service, which will allow them to connect to the internet over a server based outside the country. In response, China has tried to crack down on VPN use with the threat of fines against anyone caught using unauthorized VPN services.