Associated Press reporters at the scene saw massive plumes of yellow brown smoke filling the air above the Cathedral and ash falling on the island that houses Notre Dame and marks the center of Paris.
Videos and images of the enormous fire engulfing the medieval Catholic cathedral have flooded social media.
According to AFP news agency, the fire was noticed at about 6:50pm local time (14:50 GMT).
Firefighters believe the blaze is "potentially linked" to the renovation work of the building, reports Le Figaro.
Pedestrians are flooding the streets to watch the blaze, many in tears, one Paris resident tells PEOPLE.
The 12th Century building, immortalized in the novel The Hunchback of Notre Dame, was undergoing renovation work due to "deterioration of structural elements". Firefighters eventually were able to assemble fire boats on the river. "Emotion of an entire nation. Like all our compatriots, I'm sad tonight to see this part of ourselves burn". The cathedral is a worldwide Parisian icon and site of some of the most important moments in the history of France.
Paris mayor Anne Hidalgo in a tweet described it as a "terrible fire".
US President Donald Trump has suggested "perhaps flying water tankers" to extinguish the fire. Building began in 1160 and was completed almost a hundred years later.
I'll continue to update this story throughout the day.
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