On Monday, French President Emmanuel Macron also took to Twitter to express the structure's significance to France and pledge that it would be restored.
Located on the Ile de la Cite in the center of Paris, the Gothic cathedral attracts millions of tourists each year.
The spire atop the iconic cathedral collapsed amid the devastating fire on Monday.
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.
A massive fire has broken out at Notre-Dame Cathedral in Paris. Flames that began in the early evening burst through the roof of the centuries-old cathedral and engulfed the spire, which collapsed, quickly followed by the entire roof.
The Friends of Notre Dame foundation has even been seeking to raise a massive €150 million ($180 million) from French citizens and Francophiles in the United States to help foot the bill for a major facelift. "Happy and unfortunate events for centuries have been marked by the bells of Notre Dame".
Paris Mayor Anne Hidalgo says firefighters are trying to contain a "terrible fire" at the city's Notre Cathedral.
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A firefighter at the scene said all efforts were being directed at saving the northern tower and the artwork at the back of the cathedral.
It is not believed that anyone has been injured in the fire, but the huge historic loss is hard to fathom.
President Donald Trump, 72, suggested using "flying water tankers" to put out the massive fire at Notre Dame Cathedral in a viral tweet on April. 15, and it didn't take long for many of his followers to mock his words with various memes and other responses.
The cathedral was actively under renovation and partially surrounded by scaffolding prior to the fire.
He recalled that Notre Dame's bells sounded a death knell after the November 2015 terror attacks in Paris. The spire was undergoing renovation.
While experts said that the cathedral was not at risk of sudden collapse, many will now be fearing the worst, as parts have already collapsed.
"Notre-Dame belonged to all humanity".