Nearby buildings were evacuated as fears mounted that the structure could collapse.
"Throughout the last 900 years or so, Notre Dame has been at the heart of all the big events in French history", University of Melbourne historian Peter McPhee said.
The cathedral suffered "colossal damages", Paris Deputy Mayor Gregoire said.
Notre Dame's foundation stone was laid in 1163 by Pope Alexander III, and the cathedral was completed in the 13th century. "Our hearts are with the citizens of France and the tales of Notre Dame, true and fictional, in prayer that they will endure forever". From the scene, Mr Macron promised to rebuild the monument as "it was the destiny" of the French people.
During the French Revolution in the 18th century, the cathedral was vandalised in wide spread anti-Catholic violence: its spire was dismantled, its treasures plundered and its large statues at the grand entrance doors destroyed.
"All means are being used, except for water-bombing aircrafts which, if used, could lead to the collapse of the entire structure of the cathedral", the agency tweeted. British Prime Minister Theresa May said her thoughts were with the French people and emergency services fighting the "terrible blaze".
Heavy tapestries covered the walls to hide holes and cracks by the time Napoleon Bonaparte took power. About 12 million people visit Notre-Dame each year. From the crowning on Henry VI of England in 1431, Napoleon's crowning in 1804, and to the honoring of Joan of Arc in 1909, the cathedral's prominence in European world history is quite apparent.
1793: Revolutionaries ban Catholicism and rename Notre Dame the Temple of Reason. While Notre Dame did not charge for general admission, tourists who wished to see the bell tower or the crypt would need to pay €8.50 or €6, respectively.
The spire, like the rest of the gothic edifice, had been undergoing the 11-million-euro ($12.4-million) overhaul financed by the French state to fix damage inflicted by time, pollution and the weather.
The French Revolution was even more devastating.
What does the future hold?
"All around the world, all of us feel a certain sadness in our hearts at the thought of the people of Paris losing not only such an astonishing, most attractive cathedral in the world, but their cathedral", Thomas Cardinal Collins said.
The 12th-century Gothic church was undergoing renovation.
And yet, despite Adolf Hitler ordering that Paris be left a "heap of burning ruins", the Nazis lost control of the city in the aftermath of the Allies' D-Day landings without putting up a serious fight.
The fire, just days before Easter, was met with horror by Parisians and tourists.
The Rose Windows are a trio of huge round windows over the cathedral's three main portals. The message looked to the future, saying "the French people will rebuild it, they will raise it up again without a doubt".
Shepherd said his USA cathedral has likewise struggled to pay for its repairs since the 2011 natural disaster caused $34 million in damage (it still needed $19 million as of March) and is only halfway finished with its work.
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