A YouTube fact-check feature which is meant to tackle misinformation accidentally tagged live broadcasts of a fire engulfing Notre-Dame Cathedral in Paris with details about the 9/11 terror attacks.
The blaze erupted in the Unesco world heritage landmark in the French capital on Monday, sending its spire and roof crashing to the ground as flames and clouds of smoke billowed into the sky.
The fire, which at one point threatened the entire edifice, was brought under control early on Tuesday about nine hours after it broke out.
News outlets began live-streaming broadcasts of the fire on YouTube, but below some of the clips an unusual text box popped up - an entry from the Encyclopedia Britannica about the September 11, 2001 attacks in the United States.
In those attacks, al-Qaeda militants hijacked two passenger planes and flew them into the towers of the World Trade Center in New York, causing them to collapse, while a third hijacked jet smashed into the Pentagon. Some 3 000 people were killed.