Dozens of people were killed and around 100 injured, most of them seriously, after fire tore through a crowded bar during a New Year's Eve party in the upscale Swiss ski resort of Crans-Montana, officials said on Thursday.

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 blaze, which was initially reported as an explosion, remains unclear but authorities said it appeared to be an accident rather than an attack.

Swiss police said "tens" of people were presumed dead with around 100 injured, and the Italian foreign ministry said information from Swiss police indicated about 40 deaths. Swiss officials declined to give a specific figure.

Video footage showed lines of ambulances queuing and helicopters landing to take victims of the blast to nearby hospitals and specialist burns units in other Swiss cities.

Two young French women who said they were in the bar told France's BFM TV that they saw the fire start in the basement section of the club after a bottle containing "birthday candles" was held up too close to the wooden ceiling.

"The fire spread across the ceiling super quickly," one of the two women, who identified themselves as Emma and Albane, told BFM TV. The pair said they were able to climb a narrow staircase to the ground floor as panic broke and escape the building. Minutes later, the fire had reached the ground floor too, they said.

BFM showed video of a waitress carrying a champagne bottle with a lit 'fountain candle' through the bar, in line with the account, but the video did not show the fire taking hold.

Video footage verified by Reuters showed fire spreading from the building, with people outside the club, some of them running and screaming.

Victims from different countries
Italy's ambassador to Switzerland, Gian Lorenzo Cornado, told Sky TG24 local authorities had told him the blaze was started by someone letting off a firework inside the bar which set fire to the ceiling. He was in Crans-Montana, where he said a number of Italians had gathered seeking information about missing relatives or friends. He declined to say if there were any Italian victims.

On Thursday morning, hours after the explosion, footage from the street outside showed the area cordoned off, with forensic tents behind white screens set up in front of the bar in Crans-Montana, a fashionable ski centre with an array of boutiques, luxury hotels and restaurants.

The daytime scene, with small groups of people, some in tears or carrying flowers, was a stark contrast to the panic and confusion that officials said faced first responders who arrived when the alarm was raised.

"The first responders - the firefighters and police officers - arrived at a scene of chaos, at a dramatic scene," Stephane Ganzer, head of security for Valais canton, told reporters.

He said some of the victims were from other countries, hundreds of personnel were working on the case and a helpline had been opened for relatives. Officials said the grim task of identifying badly burned bodies would take a considerable time.

"I can't hide from you that we are all shaken by what happened overnight in Crans," the canton's head of police, Frederic 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.

Local prosecutor Beatrice Pilloud said a full investigation had been opened into the incident, at the bar, which Swiss company records indicated was owned by a French couple. "At the moment we are considering this a fire and we are not considering the possibility of an attack," she told a press conference.

Mourning
Swiss Federal President Guy Parmelin expressed shock at the scale of the disaster, which came less than a year after a fire in a club in North Macedonia killed 59 people.

"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," he said on the social media platform X, expressing condolences.

The foreign ministers of neighbouring Italy and Germany both expressed 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.

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, which is due to host next year's Alpine World Ski Championships. Authorities said 10 helicopters and 40 ambulances had been deployed.