About 40 people were killed and at least 115 seriously injured when a fire broke out during a New Year’s celebration at a crowded bar in the Swiss Alpine resort of Crans-Montana shortly after midnight.

The blaze transformed the Le Constellation bar from a festive venue into the site of one of Switzerland’s worst tragedies, prompting five days of national mourning.

Authorities said the exact death toll and number of people inside the bar remain unknown, and an investigation is underway to determine the cause, though officials stressed it was not an attack.

Survivors described scenes of chaos as flames spread rapidly, the ceiling collapsed, and people struggled to escape through narrow exits or broken windows, the AP has reported.

Among the victims were several Italian citizens, leading Italian officials to assist with medical transfers and support for affected families.