Microsoft blamed an “accidental human error” for its Bing search engine not showing image results for the query “Tank Man”.
The phrase relates to the iconic image of a lone protester standing before tanks in China’s Tiananmen Square during demonstrations in 1989.
On Friday users who searched for the term reported receiving the message: “There are no results for tank man”.
It prompted accusations of possible censorship on the protest anniversary.
“Tank Man” is often used to describe a man, who had never been identified, pictured standing before tanks in Tiananmen Square in June 1989. It became the defining image of the crackdown in which hundreds, possibly thousands, were killed.
But when users in countries including the UK, US and Singapore tried to find the image on Friday, the 32nd anniversary of the protests, it appeared to have vanished.
China heavily censors any online discussion about the Tiananmen Square crackdown. This year commemorations marking the anniversary in Hong Kong were low key after authorities banned a vigil.
Beijing is known to require search engines operating in its jurisdiction to censor results, but those restrictions are rarely applied elsewhere.
Microsoft said the issue was “due to an accidental human error and we are actively working to resolve this.”
But the director of Human Rights Watch, Kenneth Roth, said he found the idea it was an inadvertent error “hard to believe”.
Several hours after the issue was first reported, images of “tank man” had begun appearing again on Bing.
Rival Google showed many results for the famous image when the search was performed on Friday.
Microsoft Bing is one of the few foreign search engines available in China.
Authorities in China operate a firewall that blocks many US tech platforms, including Facebook and Twitter.
Both Bing and LinkedIn, another Microsoft site, have reportedly censored their content in China.
In 2019, Bing was briefly inaccessible in China, which some suggested was the result of being blocked by authorities.
Some are concerned about China’s ability to exert its political influence overseas.