Parisians watched on, many of them lost for words.
Reactions from around the world came swiftly.
He said the fire would put "a damper" on the tax round table he was about to begin. "My thoughts are with the people of France as a masterpiece of European gothic is at risk of being destroyed". It is a building that has seen centuries of history and is a symbol of France.
"Everything is burning, nothing will remain from the frame", Notre Dame spokesman Andre Finot said, according to the Associated Press. He suggested the use of "flying water tankers" on the fragile 12th-century structure and warned France "must act quickly!" And while viewers around the world watched the disaster unfold, President Donald Trump - for some reason - felt the need to chime in.
"There is no part of the building untouched by the irreparable loss of sculptural and decorative elements, let alone the alarming deterioration of structural elements", said the foundation.
1455: Joan of Arc's mother, Isabelle Romee, arrives at Notre Dame to appeal for her daughter at her trial. A presidential official said Macron was to go to the scene of the blaze.
Authorities are investigating if renovation work on the cathedral's spire was a factor in starting or spreading the fire.
"On behalf of the State of Israel, I would like to express my deepest solidarity with France and the French nation over the awful fire at Notre Dame, a world symbol of civilization", he said.
"My thoughts are with the people of France tonight and with the emergency services who are fighting the bad blaze at Notre Dame Cathedral", the British leader tweeted.
Notre-Dame has stood tall above Paris since the 1200s.
Firefighters cleared the area around the cathedral, which marks the very centre of Paris.
The peak of the church is undergoing a 6 million-euro ($6.8 million) renovation project.
The Notre Dame Cathedral is one of Paris' most popular tourist landmarks and attracts millions of visitors every year.
Notre Dame Cathedral in Paris burst into flames on April 15, engulfing the historic building and raining ash down upon people on the streets below.
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