"As firemen were looking for a gas leak in the building, a dramatic explosion took place," Interior Minister Christophe Castaner said, adding that one of the firemen had been buried under debris for several hours.
Castaner said on his Twitter feed that two firefighters had died, and that 10 people, including one firefighter, had serious injuries. Another 37 people had lighter injuries, he said. Earlier he had told reporters that two civilians had also died.
Just hours after the blast, thousands of yellow vest protesters marched noisily but peacefully through the Grands Boulevards shopping district of northern Paris, just a few hundred metres (yards) from the scene of the explosion.