Rescue workers rushed to evacuate artworks. The cathedral's bronze statues had been removed last week for repairs.
Nedjma, another witness, said she saw the fire on her way home from work. Speaking alongside junior Interior minister Laurent Nunez late Monday, Gallet noted that "two-thirds of the roofing has been ravaged".
Firefighters atop cherry picker cranes sprayed water onto the church in an attempt to calm the flames, and the smell of smoke emanated through the air. About 700 people were inside the building when the fire broke out and all got escaped unscathed, though one firefighter who was seriously injured.
Tourists and Parisians looked on aghast from the streets below.
Ligon said the cathedral had been packed with people during Palm Sunday. "Must act quickly!" Trump tweeted. It's been there for so many years and in a few minutes half of it disappeared ... insane.
In Montreal, the bells of the city's Notre-Dame Basilica rang out in solidarity this afternoon as the Paris landmark was consumed by flames. The cathedral's wooden frame was reduced to kindling as the world watched history go up in smoke.
"The history, the prayerfulness - for me, it's the center of worship", Baenziger said.
He said people are standing outside, watching and crying.
Father Manny Alvarez said he had plans to visit the cathedral in the summer. "Paris without the cathedral is not Paris anymore".
French President Emmanuel Macron speaks as Prime Minister Edouard Philippe and Archbishop of Paris, Michel Aupetit, stand near the Notre Dame Cathedral where a fire burns in Paris, France, 15 April 2019.
Curry’s 38 points lead Warriors to Game 1 win over Clippers
Ben Simmons is on the attack so far in Game 2 - he has seven points, four rebounds and three assists through one quarter. On the court, it was Lou Williams and Montrezl Harrell that made the difference, combining for 51 of the Clippers' 104.
"We'll rebuild this cathedral all together and it's undoubtedly part of the French destiny and the project we'll have for the coming years", said Mr Macron. "We pray for the firefighters and for all those who are doing everything possible to face this dramatic situation", the Vatican said.
Built in the 12th and 13th centuries, Notre Dame is the most famous of the Gothic cathedrals of the Middle Ages. Situated on the Ile de la Cite, an island in the Seine river, its architecture is famous for, among other things, its many gargoyles and its iconic flying buttresses.
The cathedral is located at the very centre of the French capital and its construction was completed in the mid-12th century after some 200 years of work.
Napoleon was crowned French emperor there in 1804.
The cathedral's spire was now undergoing renovations, but the monument's last major makeover was more than 150 years ago, partly inspired by Victor Hugo's depiction of its decaying state in his novel, "The Hunchback of Notre Dame".
The fire collapsed the cathedral's spire and spread to one of its landmark rectangular towers. He earlier canceled a planned address to the nation in which he was to announce policy measures in response to the Yellow Vest protest movement.
A massive fire engulfed parts of the Notre Dame Cathedral on Monday. Thoughts for all Catholics and for all French.
"It has survived, and will survive", and actress Marlee Matlin shared, "So sad to see history burning in Paris so I'd like try my best with a French translator to convey my thoughts: J'envoie des prieres sinceres aux gens de france (I send honest prayers to the people of France)".
Barack Obama, the former USA president, struck a more empathetic tone, saying that the cathedral was one of the "world's great treasures" before adding that he was thinking of people of France "in your time of grief".