A major fire broke out in the cathedral in the western French city of Nantes on Saturday, blowing out stained glass windows and destroying the grand organ in the 15th-century building, according to Aljazeera.

Prosecutor Pierre Sennes told reporters three fires had been started at the site and authorities were treating the incident as a criminal act. Dozens of firefighters brought the fire under control after several hours. Smoke was still coming out of the Gothic structure after massive flames earlier engulfed the inside.

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

Emergency workers roped off the area around St Peter and St Paul Cathedral, in the historical center of this city on the Loire River. The blaze comes about a year after a major fire at the Notre Dame cathedral in Paris destroyed its roof and main spire.

Local fire chief Laurent Ferlay said the fire had broken out behind the grand organ, which was completely destroyed, he said. Stained glass windows at the front of the cathedral were blown out. However, the damage was not as bad as initially feared.

It was not the first time fire has damaged the cathedral. It was partly destroyed during World War II in 1944 after Allied bombings. In 1972, a fire completely ravaged its roof. It was finally rebuilt 13 years later with a concrete structure replacing the ancient wooden roof.

“The fire of 1972 is in our minds, but at this stage, the simulation is not comparable,” Nantes Mayor Johanna Rolland told reporters.

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.”