France 24 is reporting that French historian Camille Pascal has told a local news station that the fire is destroying "invaluable heritage".
"It's been 800 years that the cathedral watches over Paris", Mr Pascal said, adding: "Happy and unfortunate events for centuries have been marked by the bells of Notre-Dame."
The vicinity surrounding Notre-Dame cathedral, which is one of Europe's most visited attractions, has been cleared by emergency services.
The building is in central Paris.
BBCCopyright: BBC
Recent renovations
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In this photo from June 2018, workers are seen repairing the wooden roofImage caption: In this photo from June 2018, workers are seen repairing the wooden roof
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Workers have been removing statues for repairs in recent daysImage caption: Workers have been removing statues for repairs in recent days
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Officials had launched an appeal for funds to repair crumbling parts of the churchImage caption: Officials had launched an appeal for funds to repair crumbling parts of the church
ReutersCopyright: Reuters
Restored angel statues were returned to the roof last weekImage caption: Restored angel statues were returned to the roof last week
'Everything is burning'
A Notre-Dame spokesman, Andre Finot, says the cathedral's wooden interior is likely to be completely destroyed by the fire.
"Everything is burning, nothing will remain from the frame," he told French media.
ReutersCopyright: Reuters
Facts about Notre-Dame
The church receives almost 13m visitors each year, more than the Eiffel Tower
Built in the 12th and 13th Centuries and currently undergoing major renovations
Last week, several statues of the facade of the Catholic cathedral were removed for renovation
The roof, which appears to have been heavily damaged by the blaze, is made mostly of wood
A major operation is under way to tackle the blaze, the cause of which is not immediately clear. No injuries have been reported.
An area surrounding the building in central Paris has been cleared.
It comes as the cathedral, which is visited by millions of people every year, is undergoing renovations after cracks began to appear in the stone, sparking fears the structure could become unstable.
Officials are using water hoses to try to extinguish the flames, but much of the fire is out of their reachImage caption: Officials are using water hoses to try to extinguish the flames, but much of the fire is out of their reach
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Getty ImagesCopyright: Getty Images
Footage of the blaze
A massive operation is under way with fire crews at the scene in central Paris.
Video content
Video caption: Notre Dame fire: Flames have broken out at the cathedral in ParisNotre Dame fire: Flames have broken out at the cathedral in Paris
Paris mayor describes 'terrible fire'
The mayor of Paris, Anne Hidalgo, described it as a "terrible fire" and has urged people in the area to respect the boundaries set up by fire crews in order to ensure that they remain safe.
A fire is spreading rapidly through the famous Notre-Dame cathedral in Paris. Flames are bursting through the roof of the 850-year-old Gothic building, engulfing the spire, which has now collapsed.
Images showed plumes of smoke billowing from the cathedral and wafting across the French capital.
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'Invaluable heritage' destroyed
France 24 is reporting that French historian Camille Pascal has told a local news station that the fire is destroying "invaluable heritage".
"It's been 800 years that the cathedral watches over Paris", Mr Pascal said, adding: "Happy and unfortunate events for centuries have been marked by the bells of Notre-Dame."
Condolences from the United States
Notre Dame University - 'Not us'
The University of Notre Dame in the US state of Indiana has tweeted that the fire is burning thousands of miles from their campus.
President Macron arrives at the scene
Area around cathedral cleared
The vicinity surrounding Notre-Dame cathedral, which is one of Europe's most visited attractions, has been cleared by emergency services.
The building is in central Paris.
Recent renovations
'Everything is burning'
A Notre-Dame spokesman, Andre Finot, says the cathedral's wooden interior is likely to be completely destroyed by the fire.
"Everything is burning, nothing will remain from the frame," he told French media.
Facts about Notre-Dame
The moment the spire fell
No injuries reported
A major operation is under way to tackle the blaze, the cause of which is not immediately clear. No injuries have been reported.
An area surrounding the building in central Paris has been cleared.
It comes as the cathedral, which is visited by millions of people every year, is undergoing renovations after cracks began to appear in the stone, sparking fears the structure could become unstable.
Last year, the Catholic Church in France launched an urgent appeal for funds to save the building.
Firefighters struggle to contain blaze
Trump suggests 'flying water tankers'
US President Donald Trump has also tweeted, suggesting that "perhaps flying water tankers" could be used to extinguish the flames.
The spire has collapsed
Macron shares sadness with nation
French President Emmanuel Macron has cancelled an address to the nation, which was due to begin later today.
He said in a tweet that he was "sad" for all of France.
Mr Macron will now be visiting the scene, an Élysée Palace official says.
Flames lick Paris skyline
Footage of the blaze
A massive operation is under way with fire crews at the scene in central Paris.
Video content
Paris mayor describes 'terrible fire'
The mayor of Paris, Anne Hidalgo, described it as a "terrible fire" and has urged people in the area to respect the boundaries set up by fire crews in order to ensure that they remain safe.
Cathedral in flames
A fire is spreading rapidly through the famous Notre-Dame cathedral in Paris. Flames are bursting through the roof of the 850-year-old Gothic building, engulfing the spire, which has now collapsed.
Images showed plumes of smoke billowing from the cathedral and wafting across the French capital.