Swiss authorities on Friday began the grim task of identifying the mostly young victims of a deadly New Year’s Eve bar fire that killed around 40 people and injured more than 100 at a ski resort in Crans-Montana.

Italian authorities said the death toll could be as high as 47, Reuters reported, citing information provided by Swiss officials. Several Italian nationals were reportedly among the dead, injured or still missing.

The fire tore through the Le Constellation bar in the Alpine resort town in the early hours Thursday, turning a packed night of celebration into panic and tragedy. Officials said the blaze appeared to be an accident rather than an attack.

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Swiss authorities said the severity of the burns suffered by many of the victims could delay formal identifications for days, as forensic teams worked to determine the identities of those killed.

Police and government officials said a large share of the victims were teenagers and young adults, with many believed to be between 16 and 26 years old. In Switzerland, the legal drinking age is 16 for beer and wine.

"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% sure," said Mathias Reynard, head of government of the canton of Valais. He said investigators were using dental records and DNA samples to identify the victims.

Italy and France said some of their nationals remain missing, and Italian Foreign Minister Antonio Tajani visited Crans-Montana on Friday and laid flowers. 

The number of Italians involved in the incident currently stands at 19, according to the BBC, which cited Italy's foreign ministry.

Australia has also confirmed that one of its nationals was injured. 

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Some survivor accounts and video broadcast on social media suggested the ceiling of the bar’s basement may have caught fire when sparkling candles used during bottle service got too close, though authorities said the cause had not yet been formally determined.

Officials said the blaze triggered the violent ignition of combustible gases — a phenomenon known to English-speaking firefighters as a flashover or backdraft, according to The Associated Press.

Axel Clavier, a 16-year-old from Paris who survived the blaze, described "total chaos" inside the bar. One of his friends died and "two or three were missing," he told the outlet.

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Clavier said he did not see the fire start but recalled waitresses entering the room carrying Champagne bottles topped with sparklers shortly before the blaze erupted.

Another witness told BFMTV that people smashed windows to escape the flames. Panicked parents rushed to the scene to see whether their children were trapped inside.

Helicopters and ambulances rushed to the scene to assist victims from multiple countries, officials said. Hospitals were quickly overwhelmed, with intensive care units and operating theaters reaching capacity.

Swiss authorities later said the burn unit in Valais was full, and that Italy made a major burns unit in Milan available to treat the injured. 

By Friday, mourners had begun leaving flowers and candles at a makeshift memorial near the cordoned-off bar as the resort town struggled to absorb the scale of the tragedy.

Fox News' Bradford Betz, Greg Norman, Emma Bussey, as well as The Associated Press and Reuters contributed to this report.