Swiss authorities say the fire broke out around 1:30 a.m. local time and rapidly engulfed the venue. CNN reports that verified video from the scene shows flames spreading quickly across the ceiling while panicked patrons tried to flee up a narrow staircase and through small exits, with some resorting to breaking windows in desperation. Witnesses told Reuters and other outlets that the crowd surged toward limited escape routes as smoke and heat built up.

Investigators now believe the blaze was likely triggered by sparklers or “fountain candle”-style pyrotechnics attached to champagne bottles, which were brought too close to the bar’s ceiling and ignited flammable materials there. Prosecutor Beatrice Pilloud said officials are reviewing video and witness testimony pointing to this as the probable cause, though the full investigation remains ongoing.

Survivors recounted scenes of chaos, with people screaming and falling as they tried to escape. One young witness told Reuters that crowds were “piled on top of each other” near exits. Many injured suffered severe burns, complicating identification efforts that authorities say could take several days.

Swiss emergency services mobilized dozens of helicopters and ambulances, and hospitals were overwhelmed. Authorities have ruled out terrorism and are assessing fire safety compliance at the venue, including materials and exit availability, as they work to understand how a night of celebration turned into a catastrophic inferno.