A four-story apartment building in a north-eastern Paris suburb has partially collapsed after an explosion, killing a child and an elderly person, authorities said.
Six more people were thought to be underneath the rubble.
Fire department spokesman Gabriel Plus said around 10 people were rescued from the disaster in Rosny-sous-Bois.
Mr Plus said emergency teams were working hard to locate people that may be still alive, using sniffer dogs in the search.
"We could still find living victims in the hours to come," he said.
Philippe Galli, Seine-Saint-Denis prefect, said the explosion was "most probably" the result of a gas leak.
Interior minister Bernard Cazeneuve arrived at the scene and pledged his support to the families and victims. He said the 22 people from the remaining two thirds of the building have been given alternative lodging.
Speaking from La Rochelle at a socialist party conference, Prime Minister Manuel Valls began his speech by sending out a "message of solidarity" to the victims.