Switzerland declared five days of mourning after an "unprecedented" fire ravaged the Le Constellation bar in the Alpine ski resort of Crans-Montana during a New Year's Eve party. The tragic event resulted in the deaths of approximately 40 people and injuries to 115, many of whom were teenagers or young adults. Swiss president, Guy Parmelin, who was in his first day as head of state, described the blaze as one of the most traumatic events in the country's history, lamenting the loss of many young lives and emphasizing the nation's commitment to preventing such a tragedy from recurring. He noted that some survivors suffered severe burns and lung damage, with Lausanne university hospital alone treating 22 patients aged 16 to 26, eight of whom required resuscitation upon arrival.

The inferno erupted around 1:30 AM. Witnesses recounted that the fire started after sparklers or flares were placed into champagne bottles, with one account describing a bartender carrying a female staff member holding one such bottle near the wooden ceiling. Other speculations suggested that charcoal from shisha pipes might have spilled, igniting the blaze. Regardless of the exact trigger, flames rapidly spread across the ceiling, quickly engulfing the crowded basement where many revelers were packed. Survivors described the terrifying speed of the fire, stating that "the whole ceiling was in flames and the fire spread really fast. It happened in seconds."

The sudden conflagration led to a chaotic escape, with screams filling the basement as people desperately tried to flee. Many surged towards a narrow flight of stairs, while others, like 16-year-old Axel Clavier, smashed windows to escape the "total chaos." Eyewitnesses described horrific scenes, with people "burning from head to foot" and lying motionless in the street. The blaze evolved into what Swiss officials termed an "embrasement généralisé," a French firefighting term for a fire that releases combustible gases which then ignite violently, similar to a flashover or backdraft.

Emergency services responded swiftly, with police arriving at 1:32 AM, just two minutes after receiving an emergency call. A red alert was issued, deploying multiple firefighting teams, 42 ambulances, and 13 helicopters to the scene. First responders prioritized victim care, directing the injured to hospitals in Sion, Lausanne, Geneva, and Zurich. Bystanders also assisted, pulling people from the intense heat and providing refuge in a nearby UBS bank branch for triage and warmth. However, the scene remained grim, with forensic teams undertaking the difficult task of identifying victims, including taking DNA samples from families.

The impact of the tragedy extended beyond Switzerland's borders, with several foreign nationals among the missing and injured. Italy's foreign ministry reported 16 nationals missing and 12 injured, while France stated eight of its citizens were missing and could not rule out French fatalities. Crans-Montana, a resort town of about 10,000 people known for its luxury and attracting wealthy Europeans, saw its picturesque setting transformed by the disaster. Le Constellation, opened in 2015 with a capacity of up to 300 people, was a popular, "cheap and cheerful" spot for younger people and tourists, including local teenagers who sometimes frequented the bar as young as 14, especially during New Year's parties when age checks were reportedly more relaxed.

The canton prosecutor for Valais, Beatrice Pilloud, confirmed an investigation was underway to identify the exact circumstances, noting the basement stairs were very narrow. She ruled out arson or terrorism as probable causes and stated it was too early to draw conclusions about emergency exits. As the community grieved, hundreds gathered in silence, laying flowers and lighting candles, while residents expressed deep worry about unaccounted friends and family. The president of the Valais canton, Mathias Reynard, conveyed his devastation, stating that what should have been a moment of celebration had "turned into a nightmare" affecting the entire country.