The Paris prosecutors' office says investigators are treating the blaze that destroyed part of Notre Dame as an accident for now.
French President Emmanuel Macron has postponed a televised speech to the nation because of a massive fire enveloping the top of Notre Dame Cathedral in Paris.
Local officials said the fire could not be battled with helicopters because dropping water from the air could have caused the entire structure to collapse, endangering surrounding buildings.
Built in the 12th and 13th centuries, Notre Dame is the most famous of the Gothic cathedrals of the Middle Ages as well as one of the most beloved structures in the world.
Cardinal Sean O'Malley was among the countless people who watched in horror Monday as news reports captured footage of a fire tearing through the roof of Notre-Dame Cathedral in Paris and toppling the centuries-old church's spire.
Flames are shooting out of the roof behind the nave of the 12th cathedral, one of the world's most visited landmarks.
Macron said a national fundraising campaign to restore Notre Dame would be launched Tuesday and he called on the world's "greatest talents" to help.
"Everything is burning, nothing will remain from the frame", Notre Dame spokesman Andre Finot told French media, according to the AP. But firefighters had struggled to take down some of the large paintings in time, he said.
"Everything is collapsing", a police officer near the scene said as the cathedral continued to burn.
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.
The fire may have been linked to renovation work being done on the cathedral. Others compared Donald's words about the fire to former President Barack Obama's words, and advised him to pay attention to what a "real president" says.
He recalled that Notre Dame's bells sounded a death knell after the November 2015 terror attacks in Paris.
"Like millions around the world we are watching closely the tragic fire engulfing Notre Dame Cathedral in Paris", O'Malley tweeted. However, the historic building was reportedly undergoing renovations.
"For 800 years the Cathedral has watched over Paris".
"I am following minute by minute the fire that is preying on Notre Dame".