About 40 people were killed and 115 injured in a blaze in at a New Year's Eve Party at an upmarket Swiss ski resort, with the disaster likened to scenes from a horror film.

This article contains details some readers may find distressing.

Most of the victims of the fire in Crans-Montana are thought to be young people, but identification of the bodies is expected to take several days at least.

The fire broke out at roughly 1.30am local time in the Constellation Bar as people celebrated the turn of the year.

Read more:
What we know about deadly Swiss fire
People 'walking on top of others' trying to escape

Emergency services were on the scene minutes later, but it was already too late to save dozens of people, thought to have been trapped in the basement.

Authorities warned that naming the victims or establishing a definitive death toll would take time due to the severity of the burns. Experts have been using dental and DNA records to try to identify the dead.

Switzerland's President Guy Parmelin described the deadly incident as "one of the worst tragedies our country has ever known", and King Charles called it a "horrific disaster".

The country will hold five days of mourning.

The cause of the blaze remains unclear, but witnesses reported seeing sparklers or candles in bottles in the basement bar.

But Beatrice Pilloud, Valais Canton attorney general, said it was too early to determine the cause of the fire. Experts have not yet been able to go inside the charred wreckage of the bar.

'Horror movie' scenes of people with hair burned off

Witnesses described scenes of panic and confusion as youngsters scrambled to escape the blaze.

Samuel Rapp, who had been at a restaurant nearby, said he saw "a lot of people at the entry trying to escape. And it was full and people [were] walking on everybody trying to escape."