A blaze killed about 40 people and injured more than 100 others in a bar at a ski resort as partygoers celebrated the arrival of the new year in the early hours of Thursday morning, Swiss police say.

On Friday, Swiss officials said the fire had likely been started accidentally by fireworks or sparklers.

Here is what we know so far.

What happened?

A fire broke out at 1:30am (00:30 GMT) at Le Constellation, a bar in the centre of the luxury Alpine ski resort town of Crans-Montana in southwestern Switzerland, police said in a statement on Thursday.

The bar is a popular tourist venue in the town. At the time of the incident, more than 100 people were present, Swiss media outlet Blick reported, quoting police.

Crans-Montana is about 200km south of the Swiss capital, Bern.

“There has been an explosion of unknown origin,” Gaetan Lathion, a police spokesperson in Wallis canton in southwestern Switzerland, told the AFP news agency on Thursday.

It is was initially unclear how the blaze began.

But on Friday, Beatrice Pilloud, the prosecutor-general of the Valais canton in southwestern Switzerland, told reporters: “Everything leads us to think that the fire was started by sparklers or fireworks placed in champagne bottles and placed too close to the ceiling.”

What do we know about the victims?

On Friday, Swiss investigators said they had begun the task of trying to identify all the victims.

The first victim named on Friday was Emanuele Galeppini, 17, an Italian junior golfer. In a statement, the Italian Golf Federation described him as a “young athlete who embodied passion and authentic values … In a time of great sorrow, our thoughts go out to his family and all those who loved him”.

Swiss officials said it could be several days before they are able to name all the victims of the fire because of the severity of their burns.

“The first objective is to assign names to all the bodies,” Crans-Montana’s mayor, Nicolas Feraud told a press conference on Thursday evening.

Mathias Reynard, head of government of the canton of Valais, said experts were using dental and DNA samples for the task. “All this work needs to be done because the information is so terrible and sensitive that nothing can be told to the families unless we are 100 percent sure,” he said.

On Thursday, Frederic Gisler, the police commander in the Valais canton in southwestern Switzerland, told reporters that about 40 people had been killed and 115 injured.

A medical source told broadcaster RTS that hospitals in French-speaking Switzerland had been overwhelmed with burn victims. Most of those injured were in serious condition, regional councillor Mathias Renard said. Police said that some victims were from other countries.

Valais hospital’s intensive care ‌unit was declared full on Thursday morning, and patients were being transferred elsewhere, he added.

On Friday, the Valais Hospital said of 55 people with “severe injuries” it had received, 13 had been able to return home and 11 remained in hospital. Four of these are in intensive care in critical condition and three are receiving surgery, the hospital reported. A further four are undergoing surgery at nearby Sierre Hospital.

Twenty-eight people in all were transferred to other Swiss or foreign hospitals.

University Hospital Zurich said it was treating 12 patients for burns.

A spokesperson at Lausanne University Hospital said its burns and intensive care units were treating 22 patients, the youngest of whom is 16 years old.

In neighbouring Italy, the major burns unit at Milan’s Niguarda hospital was made available on Thursday to treat the injured.

Italy’s ambassador to Switzerland told Italian reporters that it may take “weeks” to identify many of the victims, as their burns are so severe.

How have authorities responded?

After being alerted to the blaze, 10 helicopters, 40 ambulances and 150 responders were sent to the scene. Police said most of the injured have “significant” injuries with severe burns. Many have been taken to the Valais hospital.

The area around the bar was completely closed off to the public, and a no-fly zone over Crans-Montana was imposed.

So far, there is no information about what may have caused the fire. Specialist forensic investigators from Zurich arrived at the scene later on Thursday.

“We’re just at the beginning of our investigation, but this is an internationally renowned ski resort with lots of tourists,” Lathion, the police spokesperson, said.

However, authorities have indicated that they currently have no evidence that the fire was the result of an act of arson or sabotage.

Beatrice Pilloud, the prosecutor-general of the Valais canton in southwestern Switzerland, told the news conference, “currently we are favouring a fire and at no time is there question of any attack”.

Lathion added that a reception centre and helpline – +41 848 112 117 – have been set up to provide support to affected families. “The intervention is still ongoing,” he added.

“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,” Guy Parmelin, the president of the Swiss confederation, wrote in an X post on Thursday.

How common is an incident like this in Switzerland?

The fire at Le Constellation is likely the deadliest such incident in modern Swiss history.

Devastating fires and explosions are relatively uncommon in Switzerland.

In June 2024, two people were found dead following a blast in an underground parking garage at an apartment building in northern Switzerland, which also injured 11 people. Police told local media that the explosion had been caused by homemade fireworks.

Possibly the biggest explosion in Swiss history happened at Mitholz Ammunition Depot in December 1947, when 3,000 tonnes of Swiss army ammunition from World War II, which had been buried in the mountains above Mitholz, blew up. Nine people were killed, and several others were injured.

In February 1970, a bomb exploded on a Swissair flight bound for Israel, killing 39 passengers and nine crew members on board. It is unclear who was behind the attack. Some local media reported that a Palestine Liberation Organization (PLO) splinter group was behind the bombing, but this has never been confirmed or proven.