- Theory is someone dropped birthday cake and candles started a fire, media reports
- Most victims were between the ages of 18 and 25, report says
Initial reports indicate the fire in Rouen, Normandy, was accidental, according to the Rouen Police Department.
Following the incident, a major street was blocked and a security perimeter set up around Le Cuba Libre Bar, a witness said. Fire trucks and several police vehicles swarmed around the bar on Avenue Jacques Cartier.
Local media reported the bar was hosting a birthday party at the time, and most of the victims were between the ages of 18 and 25.
On Saturday, deputy prosecutor Laurent Labadie told the Paris Normandie publication that witnesses' statements have investigators working on the theory that someone carrying a birthday cake tripped while walking down steps and the lit candles started the fire.
"Nothing is confirmed at the moment," he said.
Initially there were reports of an explosion and a fire that followed.
French President François Hollande conveyed his condolences in a tweet. "I express my solidarity and compassion to the victims' families."
France has been on high alert following several fatal terror attacks. About two weeks ago, two jihadist attackers killed a priest in Rouen.
During Bastille Day celebrations on July 14, a man who pledged allegiance to ISIS drove a large truck through crowds gathered to watch fireworks in Nice, killing at least 85 people.