A fire is ravaging a 19th century basilica in the western French city of Nantes, and has left just a shell of the rooftop.

The fire began just after morning Mass on Monday and everyone inside was quickly evacuated, the Rev. Benoit Bertrand of the Nantes diocese told BFM television. Forty firefighters and aircraft were deployed but the flames quickly ravaged the rooftop, leaving just a shell.

"I see flames still escaping," Bertrand said.

Images of the historic basilica showed just the charred stone arches across what had been the roof, with smoke and open flames across the structure.