Trump tweeted his reaction to the blaze after video and images of huge flames and swirling smoke hovering over the historic cathedral emerged on social media. The president suggested sending flying water tankers to drown out the flames.
"So horrible to watch the massive fire at Notre Dame Cathedral in Paris. Perhaps flying water tankers could be used to put it out. Must act quickly!" wrote Trump in a tweet that has since been shared by over 25,000 people.
The president's advice drew criticism as experts argued that deploying water tankers could damage the centuries-old structure even further.
France's civil security agency said in a tweet that Parisian firefighters were doing "everything they can" to bring the fire under control, though the agency emphasized officials wouldn't use water tankers to assist in their efforts in this particular incident.
"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 group explained in a tweet, which was shared more than 7,000 times within two hours.
First Lady Melania Trump said her "heart breaks" for Parisians after seeing images of the destruction.
"Praying for everyone's safety," she concluded in the tweet.
Vice President Mike Pence offered his thoughts and prayers to the firefighters and locals.
French President Emmanuel Macron shared his thoughts with the nation and Catholics as "Our Lady of Paris" continued to erupt in flames on Monday.
"Like all our countrymen, I'm sad tonight to see this part of us burn," he wrote, in part, on Twitter.
Macron has already postponed a pre-recorded speech that was set to be aired later Monday on French TV. Macron was expected to lay out his plan to address the citizen complaints that gave rise to the yellow vest protests that have rocked France since November.
Meanwhile, Paris Mayor Anne Hidalgo called it a "terrible fire."
Canadian Prime Minister Justin Trudeau said seeing the cathedral in flames was "heartbreaking."
"Canadians are thinking of our friends in France as you fight this devastating fire," he ended the tweet.
British Prime Minister Theresa May called the fire a "terrible blaze" and extended her condolences to France.
"My thoughts are with the people of France tonight and with the emergency services who are fighting the terrible blaze at Notre Dame cathedral," she wrote.
Germany's Chancellor Angela Merkel also offered sympathy to Paris on Twitter through her spokesman Steffen Seibert.
"I am saddened to see these terrible images of #NotreDame, symbol of France and of our European culture, in flames," the tweet said, in part.
It was not immediately clear what caused the fire, though sources told Fox News it appears it was related to recent construction done at the cathedral.
Notre Dame was undergoing a $6.8 million renovation project, with some sections under scaffolding. More than a dozen religious statues were removed last week for cleaning as construction crews continued to work on the building.
This is a developing story. Check back here for updates.
Fox News' Lucia I. Suarez Sang and The Associated Press contributed to this report.