News of the blaze at the cathedral - parts of which date back to the 12th century - drew reaction from around the world, including from Prime Minister Justin Trudeau.
Although there was no evidence of a connection, France has seen a number of attacks on Catholic churches in the past year, including arson and vandalism.
Gallet said: "If it collapses, you can imagine how important the damage will be".
"My prayers are for the French people, the diocese of Paris, and everyone who will have to work hard to rebuild an global treasure, eternal and powerful", Castellanos said.
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Carlos Sainz finished a further nine seconds back for McLaren in 14th, only ahead of Antonio Giovinazzi and the Williams drivers. He was later given the all-clear, but missed qualifying because his ruined auto could not be fixed in time. "Let Sebastian by.
Merkel's office called the building a "symbol of France and of our European culture".
At around 1930 GMT, almost three hours after the fire started, a Fire Department spokesman said the next 90 minutes would be crucial in seeing if the blaze could be contained.
A Paris fire department spokesperson told Reuters that the area was being cleared and a large-scale operation was underway to address the blaze.
"September 11 attacks, also called 9/11 attacks, series of airline hijackings and suicide attacks committed in 2001 by 19 militants associated with the Islamic extremist group al-Qaeda against targets in the United States, the deadliest terrorist attacks on American soil in USA history", the panel read.
Photos and videos posted to Twitter show the flames and smoke billowing from the historic cathedral.
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El País reported that tensions rose between Assange and embassy security as he grew more eccentric during his time there. The letter to Moreno is dated 10 April 2019 - a day before Assange was taken from the country's London embassy.
A spokesman from Elysee Palace said French President Emmanuel Macron will visit the scene.
Paris deputy mayor Emmanuel Gregoire said emergency services are trying to salvage the famed art pieces stored in the cathedral. I literally just visited Notre Dame two days ago.
France's Ministry of the Interior has reported that roughly 400 firefighters were responding to the Notre Dame fire.
Prior to starting his event at Nuss Truck and Equipment to tout the tax cuts, President Donald Trump commented about the raging fire at Notre Dame Cathedral. Castellanos offered prayers to the French people and all those affected by the fire.
"Heartbreaking scenes of Notre Dame cathedral in flames", Khan said on Twitter. Notre-Dame has stood tall above Paris since the 1200s.
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Witnesses have said at least 10 shots were fired and Scotland Yard confirmed firearms and a Taser were used. When officers arrived on the scene, a auto was "driven at them", Metropolitan Police said.