Candles on a birthday cake started the fire at the Cuba Libre bar, which began around midnight on Saturday.
The polystyrene ceiling of the basement room where the celebration was taking place caught fire, according to AFP. Interior Minister Bernard Cazeneuve said more than 50 firefighters were called to the fire. An inquiry is now under way, he said. One of the injured people is in a serious condition. Terrorism has been ruled out.
The victims were mostly young people aged between 18 and 25, the Paris-Normandie news website reports (in French). An official told AFP that the polystyrene ceiling tiles released a gas which poisoned the victims: “The group was unable to leave the basement and most of the victims died of asphyxiation.”
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.
While the exact cause of the fire in Rouen remains to be determined, polystyrene or other insulation materials have been blamed for previous deadly blazes, including a nightclub fire in Bucharest last year which killed 27, 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.