A fire that appeared to have been caused by renovation work destroyed most of the roof of the Saint Donatien Basilica in Nantes, north-western France .

Nobody was injured in the blaze at the 19th Century city landmark, officials said, even though workers were on the roof when it caught fire. A fireman at the scene said the building's structure may have been left unstable.

"The inquiry will determine with certainty, but the work on the roof seems to have been the cause," the city's mayor Johanna Rolland said.

The blaze broke out after morning Mass, with worshippers evacuated from the building, Rev Benoit Bertrand said.

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.

Mayor Rolland, said the basilica was "an important symbol" for the Catholic community and she also thanked firefighters for their "rapid and brave action".

The blaze 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 were launched to save several precious objects inside the basilica, most notably its organ.

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.