Paris's mayor said Monday that city firefighters were trying to control a “terrible" blaze at the Notre Dame Cathedral.

“A terrible fire is underway at Notre Dame Cathedral in Paris. The fire brigade are trying to control the fire," Anne Hidalgo tweeted. "We are mobilized locally in close connection with church authorities. I ask everyone to respect the security perimeter.”

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The fire department in Paris said that a major operation was underway, Reuters reported.

France 2 television reported that police were treating the blaze as an accident.

Macron, Hidalgo, Prime Minister Edouard Philippe and first lady Brigitte Macron are all on the scene of the fire, accompanied by the the Paris prosecutor. The prosecutor has opened an investigation into the fire, according to CNN.

The cathedral, which was built in the 13th century, is one of the most popular tourist destinations in Paris. It attracts more than 10 million visitors a year.

Cathedral spokesperson Andre Finot told multiple outlets that the entire wooden interior of the building is on fire and will likely be destroyed.

“Everything is burning, nothing will remain from the frame,” he reportedly said.

Smoke could be seen billowing out from the top of the cathedral in photos and videos shared online.

A reporter from the Associated Press on the scene said that the fire has now spread to one of the church’s landmark rectangular towers. 

President TrumpDonald John TrumpHouse Dems demand Barr cancel 'inappropriate' press conference on Mueller report DOJ plans to release 'lightly redacted' version of Mueller report Thursday: WaPo Nadler accuses Barr of 'unprecedented steps' to 'spin' Mueller report MORE tweeted that it was "horrible" to see Notre Dame in flames, and suggested using "flying water tankers" to attack the fire.

"So horrible to watch the massive fire at Notre Dame Cathedral in Paris," he wrote. "Perhaps flying water tankers could be used to put it out. Must act quickly!"

Trump in later remarks to a crowd in Minnesota called the cathedral "one of the great treasures of the world."

"I will tell you the fire that they’re having at the Notre Dame cathedral is something like few people have witnessed," he said.

"It might be greater than almost any museum in the world. And it’s burning very badly. It looks like it’s burning to the ground," he added, noting that the structure was being renovated.

"They think it was caused by renovation," he said. "And I hope that’s the reason."

Several other prominent political figures expressed sadness on Twitter and shared their hopes that no one was hurt. 

"Notre Dame of Paris in flames. Emotion for a whole nation. Thoughts for all Catholics and for all French. Like all our countrymen, I'm sad tonight to see this part of us burn," French President Emmanuel Macron tweeted.

--This developing report was last updated at 3:23 p.m.