A fire that killed 13 people at a bar in the French city of Rouen was caused by someone carrying a birthday cake with lighted candles, police say.
Officials believe the person tripped on stairs leading to the basement.
They say soundproofing material on the ceiling of the basement at the Cuba Libre bar burned and emitted toxic gas in the early hours of Saturday.
Most of the young people who died were killed by this gas. Six others were hurt. One is in a critical condition.
Interior Minister Bernard Cazeneuve said more than 50 firefighters were called to the fire. An inquiry is now under way.
A witness told French TV that there was panic in the bar: "Everybody wanted to get out.
"Unfortunately those who were in the basement didn't have the time to get upstairs."
The victims were mostly young people aged between 18 and 25, the Paris-Normandie news website reports (in French).
Prime Minister Manuel Valls said in a tweet (in French): "Deep sadness with regard to the tragedy which mowed down 13 young lives. Compassion and support for the afflicted families."
The authorities praised firefighters for the speed of their response.
The fire is the deadliest to hit France since a series of blazes in 2005, according to French media.
The use of polystyrene insulators is prohibited in public venues in France.
Insulation materials including polystyrene have been blamed for previous deadly blazes, including a nightclub fire in Bucharest last year which killed , and a fire in a club in Brazil in 2013 which killed 241.
Most of the victims in that blaze, in the city of Santa Maria, died after inhaling toxic smoke produced when ceiling insulation foam caught fire.