"There are a lot of art works inside ... it's a real tragedy", Paris Mayor Anne Hidalgo told reporters at the scene.
Years of rain, snow and pollution were eroding the flying buttresses that prop the cathedral up, said Picaud, and that was putting the whole cathedral at risk of falling down. As the cathedral burned, Parisians gathered to pray and sing hymns outside the church of Saint Julien Les Pauvres across the river from Notre Dame while the flames lit the sky behind them.
Thousands of onlookers lined bridges over Seine and along its embankments, held at a distance by a police cordon. Castellanos offered prayers to the French people and all those affected by the fire. Macron cancelled an address to the nation that he had been due to give later on Monday evening.
Innumerable artworks and relics are located inside the building.
Notre Dame's priceless artifacts included much of the building itself, such as it's famous gargoyles, the South Rose stained glass window, and it's grand organ complete with 8,000 pipes. But firefighters had struggled to take down some of the large paintings in time, he said. Paris police said there were no reported deaths. Investigators are said to be treating the fire as an accident.
A spokesman said the entire wooden frame of the cathedral would likely come down, and that the vault of the edifice could be threatened too. France's President Emmanuel Macron will be visiting the site later, according to a government spokesperson.
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Gerald Toussaint of Mount Pleasant Baptist Church told the Daily Advertiser , noting that it was more than 140 years old. On April 2, a fire was reported at the Greater Union Baptist Church in the 1400 block of Hwy 742 in Opelousas .
He extended "thoughts for all the Catholics and all the French".
Nobody was injured, junior interior minister Laurent Nunez said at the scene, adding: "It's too early to determine the causes of the fire". During the 16th century, the Huguenots damaged statues housed in the cathedral, and during the French Revolution, in the 18th century, when Notre-Dame was used to store food, artifacts of all kinds were plundered and destroyed.
The Vatican, meanwhile, expressed its "incredulity" and "sadness" over the fire in the cathedral, which it called "a symbol of Christianity in France and across the world".
Soule and her father, Win Soule, 58, and Libby Heselton, 53, are on a weeklong trip to Paris where they planned to "see all the sights" and had just finished their visit to Notre Dame. "I see no hope for the building", said witness Jacek Poltorak told Reuters.
Notre Dame dates back to 1160 and defined the City of Paris for centuries.