French President Emmanuel Macron has vowed to rebuild Notre Dame after firefighters declared the 850-year-old world treasure's structure "saved" from ruin.
Notre Dame's spire has already collapsed, and firefighters claim its iconic rose glass windows have been destroyed in the devastating inferno.
But the French leader, speaking outside the still-smoking cathedral more than 500 firefighters had battled for hours to save, said Notre Dame would rise from the ashes.
The world leader said: “We will appeal to the greatest talents and we will rebuild Notre-Dame because that’s what the French are waiting for, because that’s what our history deserves, because it’s our deepest destiny”
He declared an international appeal would be launched to raise the funds to rebuild the Cathedral, shortly after firefighters declared the structure would survive and the two towers had been saved.
Prosecutors in France believe the fire started accidentally based on their preliminary investigation.
As crews begin to get the blaze under control, reports say a firefighter tackling the blaze was "seriously injured" amid the response to the massive fire.
Onlookers were seen singing hymns and applauding exhausted firefighters in moving scenes from Paris beaming out around the world.
Firefighters earlier claimed the 13th century stained glass windows that make the cathedral so instantly recognisable are gone.
"They exploded because of the heat of the blaze," one firefighter said.
They said the Rosette West, which was created in 1225, the Rosette North, created in 1250, and the Rosette South, which dates back to 1250 have been lost to the flames.
The final hours before they declared the structure protected were "crucial" to saving treasured landmark, a Paris Fire Department spokesman had said earlier as crews battled to contain the blaze.
Now, it appears looks like they have done just that. The Cathedral has been saved but the devastating images beaming around the world from Paris made the "colossal damage" its suffered plain to see.
The important Catholic site of worship went up in flames during Christianity's Holy Week of Easter.
"Everything is collapsing," a police officer near the scene was heard to say as Parisians and tourists watched in tears as a "symbol of Paris" burned before their eyes.
Paris Fire Chief Jean-Claude Gallet said it is unclear if city firefighters will be able to keep the blaze from spreading and causing more destruction.
Speaking outside the cathedral, he said "we are not sure we are capable of stopping the spreading" to Notre Dame's second tower and belfry.
He said: "If it collapses, you can imagine how important the damage will be."
Crowds have gathered from the River Seine's bridges and banks as emergency services try desperately to save the medieval building and the priceless works of art at its heart.
Some sang hymns as they watched the important Catholic place of worship burn.
French President Emmanuel Macron has arrived at the scene where devastating footage earlier captured the moments the spire of one of Paris' most recognisable landmarks collapsing.
The leader has arrived to speak to emergency services as the world watches the cathedral burn, prompting messages of sorrow from around the world.
Moving footage has captured crowds singing Ave Maria as they watch Notre Dame burn.
The scenes prompted a message from the Vatican, which says the fire has caused "shock and sadness."
The Vatican says it is close to French Catholics and is keeping Paris firefighters in its prayers.
It issued a statement: "The Holy See has seen with shock and sadness the news of the terrible fire that has devastated the Cathedral of Notre Dame, symbol of Christianity in France and in the world."
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