The fire, declared fully extinguished some 15 hours after it began, ravaged the 850-year-old building’s roof and caused its spire to collapse. But firefighters who worked through the night managed to save the Paris landmark’s main stone structure, including its two towers.
The cause of the fire is not yet clear.
The Paris prosecutor’s office said it was currently being investigated as an accident, with officials saying it could be linked to extensive renovation works taking place.
Meanwhile, thoughts are turning to how the Catholic cathedral will be rebuilt.
French President Emmanuel Macron vowed to reconstruct the historic building even as the fire still burned, while two French business magnates had pledged about €300m ($339m; £259m) between them by early Tuesday.
Offers of help with the reconstruction have also poured in from around the globe, with European Council President Donald Tusk calling on EU member states to rally round.
The fire began at around 18:30 (16:30 GMT) and quickly reached the roof of the cathedral, destroying the wooden interior before toppling the spire.
Fears grew that the cathedral’s famous towers would also be destroyed.
But while a number of fires did begin in the towers, French Interior Minister Laurent Nuñez said they were successfully stopped before they could spread.
By the early hours of Tuesday, the fire was declared under control, with the Paris fire service saying it was fully extinguished by 10:00 local time (08:00 GMT).
A firefighter was slightly injured while tackling the blaze, Commander Jean-Claude Gallet told BFM TV.
What is the damage?
Search teams had already begun assessing the extent of the damage when dawn broke over the French capital. The cathedral’s blackened stone and charred scaffolding were revealed to onlookers for the first time.
According to fire brigade spokesman Lt-Col Gabriel Plus “the whole of the roof has been devastated… a part of the vault has collapsed, the spire is no more”.
However, it could have been much worse. Mr Nuñez said that, had fire crews not entered the building, “without doubt it would have collapsed”, French newspaper Le Monde reported.
Photos appear to show that at least one of the cathedral’s famed rose windows has survived, although there are concerns for some of the other stained-glass windows.
Franck Riester, France’s culture minister, warned that while the principal structure had been saved, the building was still unstable.
There were already fears about its stability, after cracks appeared in the stone.
Sections of the building were under scaffolding as part of the renovations and 16 copper statues were removed last week.
What happens next?
Individuals and groups are mobilising to help rebuild Notre-Dame. Hundreds of millions of euros have already been pledged.
Billionaire François-Henri Pinault, chairman and CEO of the Kering group that owns the Gucci and Yves Saint Laurent fashion brands, pledged €100m (£86m; $113m) towards rebuilding Notre-Dame, AFP news agency reports.
Another €200m was pledged by Bernard Arnault’s family and their company LVMH – a business empire which includes Louis Vuitton and Sephora – on Tuesday morning, according to Reuters news agency.
The French charity Fondation du Patrimoine is launching an international appeal for funds for the cathedral, a Unesco World Heritage site.
Visiting the scene on Monday night, Mr Macron – who said the “worst had been avoided” with the preservation of the cathedral’s main structure – pledged to launch an international fundraising scheme for the reconstruction.
“We’ll rebuild this cathedral all together and it’s undoubtedly part of the French destiny and the project we’ll have for the coming years,” said Mr Macron.
“That’s what the French expect [and] because it’s what our history deserves,” he added, visibly emotional, calling it a “terrible tragedy”.
Offers of help have also been pouring in from around the globe, with Russian President Vladimir Putin saying he is happy to send experts to help restore the cathedral.
The British government is also looking into what it can do to help with its reconstruction, according Ed Llewellyn, the UK ambassador to France.
Spanish Culture Minister Jose Guirao said his country is also seeking ways to help – although, he added, “right now, above all, it’s about moral support, solidarity and from there, whatever they need”.
What about the cathedral’s treasures?
Emergency teams managed to rescue valuable artwork and religious items, including what is said to be the crown of thorns worn by Jesus before his crucifixion, which were stored inside the cathedral built in the 12th and 13th centuries.
A tunic, which King Louis IX is said to have worn when he brought the crown of thorns to Paris, was also saved.
“We had a chain of solidarity, especially in saving the works of art… [They] were able to be saved and put in a safe place,” said Paris Mayor Anne Hidalgo. “This is a tragedy for the whole world… Notre-Dame is the entire history of Paris.”
Historian Camille Pascal told French broadcaster BFMTV that “invaluable heritage” had been destroyed. “Happy and unfortunate events for centuries have been marked by the bells of Notre-Dame. We can be only horrified by what we see.”
How has the world reacted?
Thousands of people gathered in the streets around the cathedral, observing the flames in silence. Some could be seen openly weeping, while others sang hymns or said prayers.
Several churches around Paris rang their bells in response to the blaze, which happened as Catholics celebrate Holy Week.
“Notre-Dame is burning, France is crying and the whole world, too. It is extremely emotional,” Archbishop of Paris Michel Aupetit said.
The Vatican expressed “shock and sadness” while UK Prime Minister Theresa May described the fire as “terrible”.
Unesco said it stood “at France’s side to save and restore this priceless heritage” visited by almost 13 million visitors each year, more than the Eiffel Tower.
Germany’s Chancellor Angela Merkel called the Notre-Dame a “symbol of French and European culture”.
US President Donald Trump said it was “horrible to watch” the fire and suggested that “flying water tankers” could be used to extinguish the blaze.
In an apparent response, the French Civil Security service said that was not an option as it might result in the collapse of the entire building.
Because of the fire, Mr Macron cancelled a speech on TV in which he was due to address the street protests that have rocked France for months.