Paris public prosecutor Remy Heitz said the cathedral's fire alarms went off twice on Monday evening, beginning at 6:20pm (local time). While the cause of the fire is now unconfirmed, the cathedral's spire and most of its roof structure have reportedly been destroyed.
It is not clear what caused the blaze, although fire officials said the blaze may be linked to renovation work at the building.
Deputy Interior Minister Laurent Nuñez said the structure was in good condition "overall" but that "some vulnerabilities" had been identified in the stone vaults and the remainder of the ceiling.
With its iconic cathedral scorched but still standing, France on Tuesday launched an investigation into what triggered the Notre Dame inferno and how a fire that had probably started by accident could gut the symbol of a nation.
Quasimodo was the cathedral's bell-ringer in Victor Hugo's 1831 novel "The Hunchback of Notre Dame".
"All the 18th-century steles, the pietas, frescoes, chapels and the big organ are fine", he said. There is also little information on the condition of the cathedral's stained-glass windows and its many paintings. "The majesty of Notre Dame - the history, artistry, and spirituality - took our breath away, lifting us to a higher understanding of who we are and who we can be", she tweeted.
Paris officials said firefighters worked to save as much art work and holy objects from the 12th-century cathedral as they could.
"Those trees had been saplings in the 10th century, they were mature trees by the 12th century when they were felled".
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The measure was reportedly proposed in November in response to a migrant caravan that travelled from Central America to the US-Mexico border.
Taken aback by what she saw, Lesley Rowan shared a picture of the fire on Facebook and asked others if they saw what she saw.
"Is it possible to recreate that kind of medieval artisan work with timber on that scale?"
"This is obviously a huge challenge, a historic responsibility", Philippe said.
"We are acting as building pathologists to understand the mechanisms of decay in all our restoration projects and then develop treatments to manage these, or halt them altogether", he said. "But perhaps it can't be recreated as it was".
Air pollution has done extensive damage to the cathedral's facade, eroding the stonework and its famous gargoyles, but it has received only two million euros ($2.2m) a year in state funding - far short of what is required. They pumped water straight from the Seine, the grand river that traverses Paris and flows near Notre Dame.
"It's a very deep sadness".
For Olivier Lebib, who has lived in Paris for 40 years, it is necessary for the cathedral to be restored to its former glory.
"I hope we'll be able to rebuild. That's how we felt", said Cuff. "It was hard to imagine this could ever happen".