The main spire of the Notre Dame cathedral has collapsed in a huge blaze that has been raging since this afternoon.
The shocking moment was caught on camera by people watching from nearby squares.
Videos show the thin spire of the 850-year-old building topple as huge flames rise up the side.
French President Emmanuel Macron has cancelled his planned address to the nation as the cathedral continues to burn, sending smoke billowing out over the River Seine.
Witnesses are describing ash falling as flames burst from the burning cathedral, sparking fears for the landmark at the heart of Paris.
Emergency services are desperately trying to save any priceless works of art inside Notre Dame that can be rescued.
Paris’ deputy mayor, Emmanuel Grégoire, told BFM-TV: “From now on, a special mission has been launched to try to save all works of art that can be saved.
“Priority was given to securing the surrounding area to protect tourists and residents from the risk of collapse.”
France 2 television is reporting that police are treating the incident as an accident.
Paris firefighters have evacuated the area to fight the inferno, as crowds of onlookers watch the inferno ripping through the cathedral.
The fire broke out at Notre Dame Cathedral in central Paris this afternoon, a spokesman from the fire department said.
Smoke could be seen billowing out from the top of the medieval cathedral, as flames leapt out besides its two bell towers, a Reuters witness said.
Work started on Notre Dame in 1163 during the reign of King Louis VII and was completed in 1345.
Henry VI of England was crowned inside the cathedral in 1431 and Napoleon Bonaparte was crowned Emperor of France inside the cathedral in 1804.
It receives 12 to 13 million visitors a year.