The Vatican has expressed its shock and sadness, and in chiming in on Twitter with his version of sympathy, President Trump suggested using flying water tankers to fight the blaze - a suggestion French officials quickly brushed off saying it could collapse the entire structure of the landmark church.
Firefighters douse flames rising from the roof at Notre-Dame Cathedral in Paris.
Police have said the blaze is thought to be linked to the structure's ongoing $6.8 million renovation project.
Mayor Anne Hidalgo said in a Twitter message that firefighters are still trying to limit the fire and urged Paris citizens to respect the security perimeter set up around the cathedral. It is loved by Parisians, by French people, indeed people all around the world.
Sources told Fox News that it appears the fire was related to the construction.
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The wood-and-lead spire was built during that restoration, according to the cathedral's website.
News quickly spread about the awful fire at the historic cathedral, which is believed to have been caused by renovations, in the early morning hours of April. 15.
President Emmanuel Macron postponed a televised speech to the nation because of the stunning blaze and was going to the cathedral himself. He pledged to rebuild the church and said he would seek global help to do so.
Paris Archbishop Michel Aupetit invited priests across France to ring church bells in a call for prayers for the beloved Paris cathedral.
UK Prime Minister Theresa May has said her thoughts are "with the people of France tonight and with the emergency services who are fighting the bad blaze at Notre-Dame cathedral".
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"Notre-Dame de Paris in flames", Macron has tweeted.
Among its most celebrated art: three stained-glass rose windows, placed high up on the west, north and south faces of the cathedral.
French historian Camille Pascal told the BFM broadcast channel the fire marked "the destruction of invaluable heritage".
"For 800 years the Cathedral has watched over Paris".
A centuries-old crown of thorns made from reeds and gold and the tunic worn by Saint Louis, a 13th century king of France, were saved, Notre-Dame's top administrative cleric, Monsignor Patrick Chauvet said.
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