An arson inquiry has been launched after a fire broke out in the Gothic cathedral of the western French city of Nantes, shattering stained glass windows and sending black smoke spewing from between its towers.

Residents and tourists watched aghast, and emergency workers cordoned off the area around the St Peter and St Paul Cathedral, in the old centre of the city on the Loire River.

Prosecutor Pierre Sennes told reporters three fires had been started at the site and authorities were treating the incident as a criminal act. He gave no other details.

Firefighters warned people to avoid the area while efforts to extinguish the blaze are under way.

Local fire chief Laurent Ferlay told reporters 104 firemen were still at the site to ensure the blaze was completely under control.

The fire had broken out behind the grand organ, which was completely destroyed, he said. Stained glassed windows at the front of the cathedral were blown out.

It was not the first time fire has damaged the cathedral.

It was partly destroyed during World War Two 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.”

The fire also brought back memories of the devastating blaze in Notre Dame Cathedral in Paris last year that destroyed its roof and collapsed its spire and threatened to topple the medieval building.