Around 200 firefighters were mobilised to battle the fire that broke out after the blast and evacuate victims and residents in the area, Interior Minister Christophe Castaner told reporters at the scene.
The explosion came with the city on edge during the latest “yellow vest” anti-government demonstrations, which have often degenerated into violence and vandalism in Paris and other cities in recent weeks.
“It happened when there were people in the street, and firefighters inside,” Castaner said.
Around 100 police officers blocked off several streets in the area, home to restaurants and tourist attractions including the Musee Grevin wax museum and the popular Rue des Martyrs.
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Police also closed off streets in front of the Garnier Opera house as emergency services landed two helicopters in front of the historic building to evacuate victims.
Besides the two dead firefighters, 47 people were injured in the blast, 10 of them seriously, the Paris prosecutors office said.
The explosion occurred shortly after 9:00 am (0800 GMT) in building that housed a bakery as well as a restaurant on the ground floor in the Ninth Arrondissement.
The shockwave was felt as far as four blocks away, Commander Eric Moulin of the Paris fire service said, adding that rescuers were still searching for other victims.
“I was sleeping and woke up by the blast wave,” Claire Sallavuard, who lives on the Rue de Trevise where the explosion occurred, told AFP.
“All the windows in the apartment exploded, doors were blown off their hinges, I had to walk on the door to leave the room, all the kids were panicking, they couldnt get out of their room,” she said.
“Firefighters advised us to leave but the elevator shaft had been blown out, there was no railing, nothing, and there was too much smoke,” she added.
Rescuers eventually used a ladder to evacuate the family, who lived on the first floor.
Like an earthquake
Firefighters had been responding to an alert of a gas leak at the site when the explosion occurred, Paris prosector Remy Heitz said at the scene.
“First there was a gas leak and the firefighters arrived, then there was an explosion that caused the fire,” Heitz said.
Cars were overturned by the blast and glass and rubble was strewn across large swathes of the street as dozens of residents were treated by rescue workers.
Dozens of tourists, suitcases in hand, were evacuated from the many nearby hotels in the area, a popular weekend shopping destination for locals and visitors alike.
Other residents were in bathrobes or quickly dressing in the street as police helicopters circled overhead.
“We were sleeping when we heard the noise, it sounded like an earthquake,” a teenager who lives on a nearby street told AFP.
Many homes and buildings in Paris use gas for heating and cooking, though explosions due to leaks are relatively rare.