Hundreds of meters away, shop windows were smashed, other buildings and parked vehicles were also damaged by the force of the blast.

More than 200 firefighters and 100 police officers have been deployed. Two helicopters also landed on the nearby Place de l'Opera to evacuate victims.

The Regional Directorate of Judicial Police opened an investigation into the explosion.

"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," said Paris prosecutor Remi Heitz.