French prosecutors said they had opened an arson inquiry after fire damaged a cathedral in the city of Nantes on Saturday, noting the blaze had erupted in “three separate places.”

“An arson investigation has been opened, there are no conclusions to be drawn now because we have a lot of investigations to make which could introduce new elements,” Nantes prosecutor Pierre Sennes told AFP.

The fire erupted on Saturday morning inside the gothic cathedral in the western city, destroying the organ, but firefighters brought the blaze under control within hours.

Emergency officials added that the damage was not comparable to last year’s fire at Notre-Dame cathedral in Paris.

“The damage is concentrated on the organ, which seems to be completely destroyed. It’s platform is very unstable and could collapse,” regional fire chief General Laurent Ferlay told a press briefing in front of the cathedral.

The fire broke out early on Saturday morning inside the cathedral in the western French city of Nantes, the local fire service said on Twitter.

TV images showed smoke coming out of the 15th century structure. The blaze comes just over a year after a major fire at the Notre Dame cathedral in Paris, which destroyed its roof and main spire.

Cecile Renaud, who works in a bakery facing the cathedral and alerted the fire services early on Saturday, told BFM TV she had seen huge flames inside the building.

“It was a huge shock. It’s extremely sad.” The emergency operations center said the “major fire” was still advancing and 60 firefighters had been dispatched to the scene.

Residents and tourists watched aghast, and emergency workers cordoned off the area around the St. Peter and St. Paul Cathedral, in the historical center of this city on the Loire River. The local firefighter service warned people to avoid the area while efforts to extinguish the blaze are under way.

It is not the first time the cathedral has caught fire. It was partly destroyed during World War Two in 1944 after Allied bombings.

The gothic structure was last hit by fire in 1972. Its roof took more than 13 years to repair.

Another religious building in Nantes -- the Basilica of St Donatian and St Rogatian -- was struck by a fire in 2015 that destroyed three-quarters of its roof.

In April last year, a fire engulfed Paris's 13th century Notre-DameCathedral, causing its steeple to collapse and sending billowing fumes containing toxic molten lead into the air. The structure will take years to repair.