China has blocked Wikipedia. Facebook, Twitter, Instagram, and other social media sites have long been blocked in China. Individual Wikipedia articles about sensitive issues, such as the pro-democracy protests in Tiananmen Square and Tibet, have long been blocked in China, however, even while the main site was accessible. Suspicion of a total block on Wikipedia surfaced in late April when some Chinese Internet users took to social media to complain that the site was no longer accessible.

Possible reason for supression
Internet authorities in China often ramp up censorship before major political events or sensitive anniversaries. This June will mark 30 years since the army used force to suppress the pro-democracy protests centred around Tiananmen Square.

(Source:https://www.thehindu.com/news/international/china-blocks-wikipedia-in-all-languages/article27141724.ece)