Two firefighters have been killed and more people seriously injured when a powerful explosion caused by a gas leak tore through a bakery in central Paris on Saturday, officials said.

"Twelve people are seriously injured, including three firefighters, and 24 others have more minor injuries," Commander Eric Moulin of the Paris fire service told journalists at the scene, before two deaths were confirmed.

"Among the 12, three civilians are in life-threatening condition," he added.