In recent years France has suffered jihadist militant attacks in Paris, Nice, Marseille and beyond. But the Paris prosecutor Remi Heitz was quick to rule out foul play.
"We still need to determine the circumstances and cause of the explosion but at this stage we can say it is clearly an accident, presumably a gas leak," he told reporters.
A police source said the explosion tore apart a bakery on the rue Trevise in the Grands Boulevards district. The force of the blast shattered nearby storefronts and rocked buildings hundreds of metres away, witnesses said.
Fire brigade commander Eric Moulin told reporters that 12 people, including three firefighters, were seriously injured. Five of them, including two firemen, had life-threatening injuries, he said.
More than 200 firefighters joined the rescue operation and two helicopters landed on the nearby Place de l'Opera to evacuate victims.
"The situation is now under control," Interior Minister Christophe Castaner told reporters on the scene.
An eyewitness at a hotel nearby said he saw a huge fire erupt in the building blown out by the blast.
"There was broken glass everywhere, storefronts were blown out and windows were shattered up to the third and fourth floors," said 38-year-old David Bangura.
He said that as he approached the scene, a woman was crying for help from the first floor of a building: "Help us, help us, we have a child". (Reporting by Geert De Clercq, Caroline Paillez, Emmanuel Jarry, Simon Carraud, Lucien Libert, Christian Hartmann and Benoit Tessier Editing by Mark Heinrich/Ros Russell)
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