* The 850-year-old famous cathedral has been all but gutted in a massive blaze
* Its spire and roof have collapsed but the main structure has been saved and the fire has been stopped from spreading to the northern belfry
* A firefighter has been injured in the inferno, possibly sparked by renovation works
* 12 million people visit Notre Dame each year - it also houses famous artworks
Notre Dame cathedral will be rebuilt - "it is our destiny" - following today's devastating inferno, says French President Emmanuel Macron.
The famous Paris cathedral has been virtually destroyed in a massive blaze - its roof and spire have collapsed and firefighters have been struggling to contain the flames.
Although much of the 850-year-old cathedral has been gutted, Paris' fire chief says the main structure has been saved, with the flames stopped from spreading to the northern belfry.
Macron said the cathedral was part of France's destiny – and would be rebuilt starting tomorrow. "We will rebuild because it is what French people expect, it is what our history deserves."
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Earlier, fire authorities warned the devastating inferno "cannot be stopped". As nearby residents were evacuated for safety fears, a spokesman for the cathedral said the entire wooden frame of the cathedral would likely come down.
"Everything is burning, nothing will remain from the frame," Notre Dame spokesman Andre Finot said. The 12th-century cathedral is home to incalculable works of art and is one of the world's most famous tourist attractions.
The world-famous cathedral, which was built in 1160, was engulfed in flames after the fire broke out about 4.50am (NZT) on Tuesday.
Major parts of the 850-year-old cathedral have been destroyed in the catastrophic fire. Its spire collapsed shortly before 6am (NZT) and the blaze had spread to one of the two rectangular bell towers about 7am.
"This fire is nowhere under control - it's getting worse before our eyes," said CNN correspondent Melissa Bell. "This is so much history going up in flames."
By 6.30am, firefighters' efforts were focused on trying to save famous artworks and artefacts inside.
The immediate area surrounding the cathedral was being evacuated amid fears more of the building would collapse.
The cathedral has been undergoing a $NZ10 million renovation and French media quoted the Paris fire brigade as saying the fire is "potentially linked" to that work. Officials said the fire was accidental.
According to French newspaper Le Monde, the fire broke out in the attic of the historic monument before spreading to engulf a large section of the roof.
Prosecutors opened an investigation. Paris police said there were no reported deaths.
As the cathedral continued to burn, Parisians gathered to pray and sing hymns outside the church of Saint Julien Les Pauvres across the river from Notre Dame, as the flames lit the sky behind them.
French President Emmanuel Macron was treating the fire as a national emergency, rushing to the scene and straight into meetings at the Paris police headquarters nearby.
Macron arrived at the scene just after 7am (NZT) says the fire is taking part of everyone in France with it.
"I am sad tonight to see this part of us burning," he tweeted.
He extended "thoughts for all the Catholics and all the French".
The fire came less than a week before Easter amid Holy Week commemorations.
Claire Waddington, a Kiwi who has lived in Paris for more than 20 years, said the sight of the fire had broken her heart.
"We're all in shock," she said in a series of tweets.
She said the "catastrophic" fire had left her "shaking in shock" and that there was a strong smell of burning in the city.
"The damage that must be done, it's unthinkable," she said. "My heart is just broken."
Paris Mayor Anne Hidalgo labelled the fire "terrible".
Hidalgo urged residents of the French capital to stay away from the security perimeter around the Gothic-style church. The mayor says city officials are in touch with Roman Catholic diocese in Paris.
Macron cancelled a speech he was due to give to make his way to the scene.
A spokesperson for the cathedral said the blaze was first reported at 4.50am (NZT) (6.50pm local time) and the building was evacuated soon after.
Christine Moreau, a local resident, broke into tears as she described her horror when she saw smoke and flames coming from the roof.
"It's tragic. I can't believe this is happening. Notre Dame is part of the heart of Paris and part of our hearts too. Why couldn't more have been done to put out the blaze?"
Officials said they had not used helicopters or aircraft to fight the fire because of fears for people's safety in the immediate area.
Notre Dame - which means 'Our Lady' - was built in 1160 and completed by 1260, and has been modified on a number of occasions throughout the century.
Notre Dame is one the finest example of French Gothic architecture in Europe, and one of the most popular buildings in the world, with more than 12 million visitors a year.
Built in the 12th and 13th centuries, it is the most famous of the Gothic cathedrals of the Middle Ages as well as one of the most beloved structures in the world.
Situated on the Ile de la Cite, an island in the Seine river, the cathedral's architecture is famous for, among other things, its many gargoyles and its iconic flying buttresses.
Among the most celebrated artworks inside are its three stained-glass rose windows, placed high up on the west, north and south faces of the cathedral.
Its priceless treasures also include a Catholic relic, the crown of thorns, which is only occasionally displayed, including on Fridays during Lent.
The cathedral was immortalised in Victor Hugo's The Hunchback of Notre Dame, published in 1831, and has long been a subject of fascination in popular culture as well as the traditional art world.
On Thursday, 16 religious statues were removed from the peak for the first time in over a century to be taken for cleaning and therefore escaped the blaze.
French writer and historian Camille Pascal says the fire has caused "the destruction of invaluable heritage" and "we can be only horrified by what we see".
Pascal told French broadcaster BFMTV: "It's been 800 years that the Cathedral watches over Paris" and its bells pealed for both "happy and unfortunate events."
He recalled that Notre Dame's bells sounded a death knell after the November 2015 terror attacks in Paris.
US President Donald Trump tweeted about the fire and made suggestions for how first responders should tackle it:
French police say water planes were not used to douse the flames due to safety concerns, according to Le Monde.
The deputy mayor of Paris says the cathedral has suffered "colossal damage".
Speaking to BFMTV, Deputy Mayor Emmanuel Gregoire said first responders were now trying to salvage the art and other priceless pieces stored in the cathedral.
A cathedral spokesman has said the entire wooden interior of the Notre Dame is burning and likely to be destroyed.
"The smoke is blowing over the south side of the city towards the Tour Eiffel," witness Anne-Sophie Faivre, a 21-year-old Warwick University student on her year abroad in Paris, told the UK's Daily Telegraph.
"You can't quite smell the smoke but it's definitely in the air and the doesn't seem to be any let-up in it coming from the cathedral.
"As you can imagine there are a lot of people both tourists and locals who have gathered to watch."
Ainsley Duyvestyn-Smith, a Kiwi photographer living in Paris about 4km away from Notre Dame, said she had just popped out for takeaway pizza when she saw "clouds and clouds of white smoke" billowing into the sky.
But it was not until she got home and saw the news that she realised the fire was at the cathedral.
Duyvestyn-Smith said she had done lots of photo shoots at the iconic spot.
"It is a really popular spot for photos, especially at the moment because all the cherry blossoms are out," she said. "It is a really beautiful area."
The fire was "awful and devastating for Paris because Notre Dame is such a huge part of the architecture and history".
"From the looks of the photos the fire is in the oldest part of the building and that is almost 1000 years old, and there is also Jesus' Crown of thorns in there as well."
"So a lot of religious people are having a freak out about that being destroyed and lots of really important artefacts in there as well."
Kiwi expat Lydia Laulala, who is living in in France with her husband who plays for a French rugby team, didn't see the blaze but ran past Notre Dame yesterday as part of the Paris Marathon.
"It is very lucky [the fire] didn't happen yesterday because there was 55,000 people running around the city on the roads, so the whole city was closed down," she said.
"It would have been a logistical nightmare if it had happened yesterday."