Fire erupted inside a 19th century church in Western France Monday just after morning mass.
Worshippers had to flee the Saint-Donatien basilica in Nantes as the flames tore through the historic building.
Two workers also escaped from the roof unharmed.
They were waterproofing the building when the fire erupted.
Investigators are trying to determine if their work may have sparked the blaze.
The church is now trying to salvage precious items from inside the basilica.