Six bodies have been found after an explosion flattened a four-storey apartment building in the southern French city of Marseille.

Officials said two others remained unaccounted for and rescue efforts continued in the La Plaine district. A firefighter told AFP news agency the search for survivors was a “race against the clock”.

The cause remains unclear, but investigators are looking into the possibility of a gas leak. The blast occurred at 00:49 local time on Sunday.

Housing Minister Oliver Klein described the discovery of the bodies as “gruesome, difficult and dramatic”, and told reporters the government would support the families of the victims.

Five people from neighbouring buildings sustained minor injuries in the explosion and around 200 people had to be evacuated from their homes. Two nearby blocks partially collapsed a few hours later, but there were no further reports of injuries from this.

The mayor of Marseille, Benoit Payan, warned there was still a risk that nearby buildings could collapse.

Around 100 firefighters attended the scene to tackle a blaze that burned under the rubble throughout Sunday.

The fire hampered progress and made it difficult for sniffer dogs to detect survivors or bodies. The building is believed to have had one apartment on each storey.

In a brief statement announcing the discovery of the bodies, the fire department said that “given the difficulties of intervention, the extraction [of the bodies from the site] will take time”. A local gymnasium and two schools have been opened to accommodate the people who have had to leave their homes. Psychological support is also being offered.

French President Emmanuel Macron said on Twitter that he was “thinking of those affected and their loved ones” and thanked the emergency workers for their efforts.

Mayor of Marseille Benoît Payan said rescuers remained “determined” to find people alive. “Hope must hold us,” he said. Deputy Mayor Yannick Ohanessian told reporters at the scene that “several” witnesses had described a “suspicious smell of gas”.

Interior Minister Gerald Darmanin visited the scene on Sunday, followed by Housing Minister Olivier Klein on Monday.

In 2018, housing standards in Marseille came under scrutiny after two dilapidated buildings in the working class district of Noailles collapsed, killing eight people.

Following that incident, charities estimated that 40,000 people in the city were living in poorly-built homes, but on Sunday officials appeared to rule out structural issues as a cause of the latest collapse.