Notre Dame Cathedral has gone up in flames in a blaze that devastated the Parisian landmark, collapsing the roof and main spire of the 850-year-old building.
Flames that began in the early evening burst rapidly through the roof of the centuries-old cathedral and engulfed the spire, which collapsed, quickly followed by the entire roof.
An AFP correspondent posted images of the moment the spire of the ancient cathedral fell.
One firefighter was seriously injured - the only reported casualty. Firefighters battled smoke and falling drops of molten lead as they tried to rescue some of Notre Dame's treasures.
"Everything is collapsing," a police officer near the scene said as the entire roof of the cathedral continued to burn.
About three hours after the fire broke out, flames were seen in one of towers at the end of the building.
Four hours after the first flames were seen, Paris fire chief Jean-Claude Gallet said the cathedral's main structure had been saved from complete destruction.
Junior interior minister Laurent Nunez, who'd said fire services weren't sure they could stop the blaze, later said there was more optimism that Notre Dame could be saved.
A firefighter at the scene told Reuters efforts were being directed at preventing the collapse of the northern tower and saving the art work at the back of the cathedral.
According to drone footage taken by police, three quarters of the cathedral was still ablaze as darkness fell.
"Basically the whole rooftop is gone. I see no hope for the building," said witness Jacek Poltorak, watching the fire from a fifth-floor balcony two blocks from the southern facade of the cathedral, one of France's most visited places.
But standing in front of the burning landmark, President Emmanuel Macron pledged to rebuild the cathedral.
"Notre Dame is our history, our literature, part of our psyche, the place of all our great events, our epidemics, our wars, our liberations, the epicentre of our lives," he said.
"Let's be proud, because we built this cathedral more than 800 years ago, we've built it and, throughout the centuries, let it grow and improved it. So I solemnly say tonight: we will rebuild it together."
"The worst has been avoided, even if the battle has not been totally won yet," Mr Macron said shortly before midnight, as firefighters worked to further cool some of the interior structures still at risk of collapse.
Firefighters evacuated buildings on Ile de la Cite, the island in the River Seine where the cathedral sits and which marks the centre of Paris.
Thousands of onlookers lined bridges over the Seine and along its embankments, held at a distance by a police cordon. Some sang Ave Maria, with others in the crowd also kneeling and praying.
It was not immediately clear what had caused the fire. France 2 television reported that police were treating the incident as an accident. French media quoted the Paris fire brigade as saying the fire is "potentially linked" to a 6 million-euro renovation project on the church's spire and its 250 tons of lead.
The wood and lead spire was built during a restoration in the mid-19th century, according to the cathedral's website. Some sections of the cathedral are under scaffolding, while bronze statues were removed last week for works.
Catholic churches responded to a plea from the Archbishop of Paris to all priests in Paris to ring bells as a gesture for the Cathedral.
The Vatican said the fire at the "symbol of Christianity in France and in the world" had caused shock and sadness and said it was praying for the firefighters.
New Zealand Prime Minister Jacinda Ardern said the country's hearts were with the people of France.
"I first saw Notre Dame in my twenties as a tourist. It is breathtaking.
"While we may not have the long history that Paris has embedded within its buildings, we have experienced the devastation of seeing historic places damaged and lost. Notre Dame represents so much to so many."
'Invaluable heritage' destroyed
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.
The church is home to incalculable works of art and is one of the world's most famous tourist attractions.
A centuries-old crown of thorns made from reeds and gold and the tunic worn by Saint Louis, a 13th century king of France, were saved, Notre Dame's top administrative cleric, Monsignor Patrick Chauvet said. But firefighters had struggled to take down some of the large paintings in time, he said.
French historian Camille Pascal told BFM broadcast channel the fire was destroying "invaluable heritage."
"It's been 800 years that the Cathedral watches over Paris", Mr Pascal said. "Happy and unfortunate events for centuries have been marked by the bells of Notre Dame."
He recalled that Notre Dame bells sounded the death knell following the 2015 Paris attacks.
"We can be only horrified by what we see", Mr Pascal said.
A centre of Roman Catholic faith, over the centuries Notre Dame has also been a target of political upheaval.
It was ransacked by rioting Protestant Huguenots in the 16th century, pillaged again during the French Revolution of the 1790s and left in a state of semi-neglect. Hugo's 1831 work led to revived interest in the cathedral and a major - partly botched - restoration that began in 1844. The wood and lead spire was built during that restoration, according to the cathedral's website.
UNESCO said in a tweet it was "closely monitoring the situation and is standing by France's side to safeguard and restore this invaluable heritage".
German Chancellor Angela Merkel called the cathedral a "symbol of France and our European culture". British Prime Minister Theresa May said her thoughts were with the French people and emergency services fighting the "terrible blaze".
Paris correspondent Peter Allen told Morning Report firefighters were not using helicopter drops because the weight of the water would cause even more damage.
How the fire unfolded:
Around 6.50pm local time (4.50am NZT) : Fire starts in roof of Notre Dame Cathedral, according to firefighters. About 20 minutes later smoke could be seen from the roof.
7.40 pm: Fire spreads to the giant spire of the cathedral.
7.53 pm: Cathedral's spire collapses.
7.59 pm: French president's office says Macron is rushing to the scene.
8.07 pm: Entire roof of Notre Dame Cathedral collapses, according to a Reuters correspondent at the scene.
8.25 pm: Ile de la Cite, the island on which Notre Dame sits, is evacuated by police.
- Reuters / BBC / AP