Notre-Dame, Paris – The cause of the blaze was not immediately clear, but officials say that it could be linked to renovation work.
Images on social media show plumes of smoke billowing into the air above the 850-year-old Gothic building.
Smoke billowed from the top of the cathedral as flames ripped through its roof and bell towers.
Last year, the Catholic Church in France launched an urgent appeal for funds to save the cathedral, which was starting to crumble.
The cathedral, which dates back to the 12th century and is famous for featuring in Victor Hugo’s classic novel “The Hunchback of Notre-Dame,” attracts millions of tourists every year.
A major operation is currently under way to tackle the blaze, which broke out on Monday afternoon. An area surrounding the building in central Paris has been cleared, officials said.
The mayor of Paris, Anne Hidalgo, described it as a “terrible fire” and urged people at the scene to respect the boundaries set up by fire crews in order to ensure that they remain safe.
This story is developing. Please check back for updates.
–BBC contributed to this report.