French President Emmanuel Macron has vowed to rebuild the medieval cathedral of Notre-Dame after a major fire partially destroyed the Paris landmark.
Firefighters managed to save the 850-year-old Gothic building's main stone structure, including its two towers, but the spire and roof collapsed.
The fire was declared under control almost nine hours after it started.
The cause is not yet clear but officials say it could be linked to extensive renovation works underway.
The Paris prosecutor's office said it was currently being investigated as an accident. A firefighter was lightly injured while tackling the blaze, Commander Jean-Claude Gallet told BFM TV.
The fire began at around 18:30 (16:30 GMT) and quickly reached the roof of the cathedral, destroying its stained-glass windows and the wooden interior before toppling the spire.
Fears grew that the cathedral's famous towers would also be destroyed by the blaze.
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, although it is expected to take several days to be completely extinguished.
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.
Franck Riester, France's culture minister, warned that while the principal structure had been saved, the building was still unstable.
What happens next?
Already, 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".
Sections of the building were under scaffolding as part of the renovations and 16 copper statues had been removed last week. Work began after cracks appeared in the stone, sparking fears the structure could become unstable.
Mr Macron said the cathedral was "for all French people", including those who had never been there, and praised the "extreme courage" of the 500 firefighters involved in the operation.
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.