A huge fire has destroyed part of the 19th Century basilica of Saint-Donatien in the French city of Nantes.
The blaze broke out on Monday after morning Mass, with worshippers evacuated from the building, Rev Benoit Bertrand told local media.
Around 40 firefighters worked to extinguish the flames, which are believed to have originated on the roof where work was being carried out.
Two workers escaped from the top of the building unharmed.
The Mayor of Nantes, Johanna Rolland, said the basilica was "an important symbol" for the Catholic community.
In a statement on Facebook (in French) she also thanked firefighters for their "rapid and brave action".
The blaze broke out at around 10:30 local time (08:30 GMT) and may have been linked to "waterproofing work", according to the city's chief fire officer.
The roof and the back part of the basilica - where some wooden beams have given way - have been severely damaged and efforts are now under way to save several precious objects inside the basilica, most notably its organ.
Brendon Jeffreys, who works at the University of Nantes, witnessed the fire take hold.
"Initially, it consisted of huge plumes of smoke coming from the tower, but after a few minutes the flames started poking through and taking hold of the roof," he told the BBC.
"Many of the passers-by were visibly upset. The most frequent comment that I overheard was 'la vache', an expression of disbelief."
Social media users shared images of the burning building on Twitter, showing smoke billowing from its rooftop.
The basilica dates back to the 19th Century and is dedicated to the religious martyrs St Donatien and St Rogatien.
Another of the city's religious sites, Nantes Cathedral, suffered similar damage during a fire in 1972. It has since been restored.