A fire erupted Saturday inside a gothic cathedral in the western French city of Nantes, but firefighters brought the blaze under control within hours, emergency services said.

Officials said the cathedral's organ was destroyed and its platform could also collapse, but added that the damage was not comparable to last year's fire at Notre-Dame Cathedral in Paris.

Prosecutor Pierre Sennes told reporters three fires had been started at the site and authorities were treating the incident as a criminal act. And an investigation had been launched.

The city's fire department was alerted before 08:00 a.m. (0600 GMT) and around 100 personnel rushed to the scene.

The fire has blown out the cathedral's stained glass windows and destroyed the grand organ. And the smoke was still coming out of the 15th-century structure late on Saturday morning.

Following the incident, French Prime Minister Jean Castex said he would visit the scene later on Saturday.

"I want to know what happened, but first, I'm going to show my solidarity with the people of Nantes," Castex told reporters.

President Emmanuel Macron tweeted his "support for our firefighters who are taking all the risks to save this gothic jewel".

The blaze comes just over a year after a major fire destroyed the roof and main spire of the Notre Dame Cathedral in Paris.

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

In 1972 a fire completely ravaged its roof. It was rebuilt 13 years later.