Notre Dame cathedral in Paris engulfed in major fire

"The Notre Dame [cathedral] is among the most lovely of Paris's symbols and of France's in general, but also one of the most important to any cultured person", Rivlin said in a tweet.

It was not immediately clear what had caused the fire.

Pictures posted on social media showed enormous plumes of smoke billowing into the city's skyline as firefighters rushed to the historic site.

Last year, the Catholic Church in France appealed for funds to save the building, which was crumbling. The Associated Press is reporting that Paris police say the cause of the fire is unknown and no deaths have been reported.

The sight stopped pedestrians in their tracks along the Seine River, which passes under the cathedral.

French President, Emmanuel Macron, has cancelled a planned public address.

But what is known is that Notre Dame is irreplaceable, with a history as grand as the spire that collapsed in the blaze.

"This fire is nowhere under control - it's getting worse before our eyes", said CNN correspondent Melissa Bell. We are mobilized locally in close connection with church authorities. "I ask everyone to respect the security perimeter".

The president said his thoughts were with all Catholics and all French people. "Must act quickly!" Trump wrote on Twitter.

The French Gothic building is remarkable for its stained-glass rose window, flying buttresses and large spire.

Paris police say fighters are inside the cathedral working to put the flames out while others work from the exterior.

"I am sad to see this part of us burn", he said on Twitter.

Ed Llewellyn, Britain's ambassador to France described the images of the burning Cathedral as "heartbreaking" adding, "All our thoughts with the heroic firefighters as they battle this bad blaze". President Emmanuel Macron has expressed the shock of a "whole nation" at the fire. The building was completed around 1260, but has been modified over the centuries.

Germany's Chancellor Angela Merkel has offered her support to the people of France, calling Notre-Dame a "symbol of French and European culture".