Here's what to know about a deadly fire at a Swiss Alpine bar's New Year celebration

CRANS-MONTANA, Switzerland — Swiss investigators are probing what caused a fire in a bar at an Alpine ski resort that left dozens of people presumed dead and another 100 injured during a New Year's celebration.

Most injuries, many of them serious, occurred when the blaze swept through the crowded bar less than two hours after midnight Thursday in southwestern Switzerland.

The Crans-Montana resort is best known as an international ski and golf venue. Overnight, its crowded Le Constellation bar morphed from a scene of revelry into the site of potentially one of Switzerland's worst tragedies.

Crans-Montana is less than 5 kilometers (3 miles) from Sierre, Switzerland, where 28 people, including many children, were killed when a bus from Belgium crashed inside a Swiss tunnel in 2012.

Here's what we know about the deadly fire:

A frantic attempt to escape

The blaze broke out around 1:30 a.m. Thursday inside the Le Constellation bar amid the holiday celebration.

He said he hadn't seen the fire start, but did see waitresses arrive with champagne bottles with sparklers, he said.

Two women told French broadcaster BFMTV they were inside when they saw a male bartender lifting a female bartender on his shoulders as she held a lit candle in a bottle. The flames spread, collapsing the wooden ceiling, they told the broadcaster.

People frantically tried to escape from the basement nightclub up a narrow flight of stairs and through a narrow door, causing a crowd surge, one of the women said.

A young man at the scene said people smashed windows to escape the fire, some gravely injured, reported BFMTV. He said he saw about 20 people scrambling to get out of the smoke and flames, likening what happened to a horror movie.

The injured were so numerous that the intensive care unit and operating theater at the regional hospital quickly hit full capacity, said Mathias Reynard, head of the regional government of the Valais Canton.

While officials said Thursday it was too early to determine the fire's cause, investigators have already ruled out that it could have been an attack.

Experts have not yet been able to go inside the wreckage, said Beatrice Pilloud, Valais Canton attorney general, at a news conference.

Work is underway to identify the victims and inform their families.

''Several tens of people'' are feared dead, Gisler added.

The blaze triggered a flashover or backdraft

Victims suffered from serious burns and smoke inhalation. Some were flown to specialist hospitals across the country.

Authorities urged people to show caution in the coming days to avoid any accidents that could require the already overwhelmed medical resources.

A top venue for the world's best athletes

With high-altitude ski runs rising around 3,000 meters (nearly 9,850 feet) in the heart of the Valais region's snowy peaks and pine forests, Crans-Montana is one of the top venues on the World Cup circuit.

The resort will host the best men's and women's downhill racers, including Lindsey Vonn, for their final events before the Milan Cortina Olympics in February.

__