Flames jumped up the ornate spire before it collapsed onto the blaze-engulfed roof, sending smoke billowing out into the evening skyline of the French capital. France's President Emmanuel Macron will be visiting the site later, according to a government spokesperson.
Sources told Fox News that it appears the fire was related to the construction. The cathedral was undergoing renovation, and the assumption right now is that the fire was related to the ongoing work.
The monument sees over 13 million visitors a year and is Paris's most visited attraction, beating the Eiffel Tower, according to the city's tourism report.
"It will never be the same" said 30-year-old Samantha Silva, tears welling in her eyes as she explained how she would always take foreign friends visiting Paris to the cathedral.
A Notre Dame spokesman said earlier that the church's entire wooden interior was in flames.
In addition to being a Catholic cathedral where Mass is offered daily, Notre Dame is also an extremely popular tourist spot owing to its architecture and historical significance. "Our thoughts and prayers are with the firefighters on the scene and all the people of Paris", Vice President Mike Pence tweeted.
The cause of the fire had not yet been determined Monday afternoon.
Both the spire and roof of the cathedral have completely collapsed, and the fire has spread to one of the building's square towers.
Macron tweeted "emotion of a whole nation" on seeing Notre-Dame ablaze.
The Archbishop of Toronto said Monday the fire that heavily damaged Notre Dame Cathedral in Paris is a tragic event that has touched people everywhere.
Notre Dame's priceless artifacts included much of the building itself, such as it's famous gargoyles, the South Rose stained glass window, and it's grand organ complete with 8,000 pipes. "I see no hope for the building", said witness Jacek Poltorak, watching the fire from a fifth-floor balcony two blocks from the southern facade of the cathedral, one of France's most visited places.
The cathedral went up in flames on Monday in a roaring blaze that devastated the Parisian landmark, a huge loss for the city and for France.
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 centre of Paris.