French President Emmanuel Macron said after the French capital's fire chief announced the emergency response had changed into a monitoring and mop-up operation, "The worst has been avoided although the battle is not yet totally won."

Flames and black smoke were seen shooting from the base of the medieval church's spire on Monday.

As Paris firefighters battled the blaze, part of the spire of the 12-century monument collapsed.

Paris police said there were no deaths so far and the origin of the fire was unknown. French media quoted the Paris fire brigade saving the fire is "potentially linked" to a 6 million-euro ($9.06 million) renovation project on the church's spire and its 250 tons of lead.

Paris Mayor Anne Hidalgo says firefighters are trying to contain a "terrible fire" at the city's Notre Cathedral.

An AP reporter at the scene of Monday's fire says the roof at the back of the cathedral, behind the nave, was in flames and yellow-brown smoke and ash fill the sky.

Hidalgo urged residents of the French capital to stay away from the security perimeter around the Gothic-style church. The mayor says city officials are in touch with Roman Catholic diocese in Paris.

The fire chief in Paris said originally that it was unclear if city firefighters would be able to keep a fire at Notre Dame from spreading and causing more destruction.

Fire Chief Jean-Claude Gallet said outside the iconic cathedral as his crews battled the blaze from both the exterior and interior: "We are not sure we are capable of stopping the spreading" to Notre Dame's second tower and belfry.

Gallet said: "If it collapses, you can imagine how important the damage will be."

Flames reached one of Notre Dame's towers and brought down the church spire that extended 96 meters high.

Emmanuel Macron has promised to rebuild Notre Dame Cathedral and says he is seeking international help to restore the Paris landmark.

Macron said after the French capital's fire chief announced the emergency response had changed into a monitoring and mop-up operation, "The worst has been avoided although the battle is not yet totally won."

Macron said a national fundraising campaign to restore Notre Dame would be launched Tuesday and he called on the world's "greatest talents" to help.

The French leader credited the "courage" and "great professionalism" of firefighters with sparing Notre Dame's facade and two landmark towers from being destroyed.