Around 40 people have been killed and 100 injured, most of them seriously, after an explosion tore through a crowded bar during a New Year’s Eve party in the upscale ski resort of Crans-Montana, Swiss officials said on Thursday.

A fire broke out at 1.30 am (0030 GMT) in a bar called “Le Constellation” in the resort in southwestern Switzerland. The cause of the blast remains unclear, but authorities said it appeared to be an accident.

"At the moment we are considering this a fire, and we are not considering the possibility of an attack," prosecutor Beatrice Pilloud told a press conference, adding that authorities had opened a full investigation.

Some of the victims are from other countries, said Stephane Ganzer, head of security for the Valais canton. The canton's head of police, Frederic Gisler, said a helpline had been opened for relatives.

"I can’t hide from you that we are all shaken by what happened overnight in Crans," Gisler told the press conference.

"Our count is about 100 injured, most seriously, and unfortunately, tens of people are presumed dead," he said, adding that patients had been dispatched to hospitals in Sion, Lausanne, Geneva and Zurich.

The Italian foreign ministry said information from Swiss police indicated about 40 deaths, but Gisler declined to give a specific figure.

Earlier, police said many people were being treated for burns and that the area had been completely closed off, with a no-fly zone imposed over Crans-Montana. Authorities said 10 helicopters and 40 ambulances had been deployed.

"What was meant to be a moment of joy turned, on the first day of the year in Crans-Montana, into mourning that touches the entire country and far beyond,"Swiss Federal President Guy Parmelin said on X, expressing condolences.

Prosecutor Pilloud said authorities were trying to get the bodies of the victims to their families.

"A lot of resources have been put into forensics to identify the victims. These resources are intended to allow us to get the bodies to the families as soon as possible," she said.

Italian Foreign Minister Antonio Tajani said the fire may have been caused by fireworks.

"It seems to have been an accident caused by a fire, by some explosion, by some firecracker thrown during New Year's celebrations," he told Italy's Sky TG24 tv channel.