Interior Minister Christophe Castaner confirmed two firefighters died and 10 people, including one firefighter, had sustained serious injuries. Another 37 people had non-serious injuries, he said. The number of injured people has increased since then, with many outlets reporting 50 injured.
El Pais is reporting a Spanish woman was confirmed dead.
"As firemen were looking for a gas leak in the building, a dramatic explosion took place," Castaner said, adding that one of the firemen had been buried under debris for several hours.
An eyewitness at a hotel nearby said he saw flames envelop the ground floor of 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".
The accident at the Hubert bakery at No 6 Rue de Trevise in Paris occurred as the city undergoes a security lockdown for the ninth consecutive Saturday of yellow vest protests, with large parts of the French capital blocked off by riot police. Roughly 80,000 police are expected to be on duty Saturday.
Just hours after the blast, thousands of yellow vest protesters marched peacefully through the Grands Boulevards shopping district of northern Paris, just a few hundred yards from the scene of the explosion.
In recent years, France has suffered a string of deadly Islamist militant attacks in Paris, Nice, Marseille and elsewhere but authorities quickly clarified the blast was not a terrorist attack.
"A this stage we can say it (the gas blast) is clearly an accident," Paris prosecutor Remi Heitz said.
A police source said the explosion tore apart a bakery on the rue Trevise and witnesses said the force of the blast shattered nearby storefronts and rocked buildings hundreds of meters away.
More than 200 firefighters joined the rescue operation and two helicopters landed on the nearby Place de l'Opera to evacuate victims. Ambulances struggled to access the blast area because of police barriers set up to contain protesters.