Swiss police said on Thursday that 40 people were killed and about 100 others injured after an explosion and fire ripped through a bar crowded with New Year’s Eve revelers at the Crans-Montana ski resort in southwestern Switzerland.

The incident occurred at around 1:30 a.m. local time (0030 GMT) at the “Le Constellation” bar, police said.

Prosecutor Beatrice Biu said authorities are treating the incident as a fire rather than a deliberate attack.

Valais regional police chief Stefan Ganzer said some of the victims were foreign nationals, adding that investigations are ongoing to determine the cause of the explosion.