MARSEILLE — Two bodies have been found after an explosion flattened a four-story apartment building in the southern French city of Marseille.

Local authorities said six people remained unaccounted for and that rescue efforts were ongoing.

The blast occurred in the La Plaine neighborhood at 00:49 local time on Sunday (23:49 BST on Saturday).

The cause remains unclear, but investigators are looking into the possibility of a gas leak.

Five people from neighboring 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 without causing any additional injuries.

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 rescuers to deploy sniffer dogs, although authorities said on Sunday evening that the blaze was showing signs of abating.

The building is believed to have had one apartment on each story, and city officials said earlier that the people missing included a "young couple".

Rescue operations continued into the early hours of Monday with the help of a crane and lights.

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.

One local told French media that they heard an explosion "unlike anything I've ever heard".

Speaking to the AFP news agency, Saveria Mosnier, who lives nearby, said: "I was sleeping and there was this huge blast that really shook the room. I was shocked awake as if I had been dreaming."

She added that "we very quickly smelled a strong gas odour that hung around. We could still smell it this morning".

Deputy Mayor Yannick Ohanessian told reporters at the scene that "several witnesses have reached us this morning to say there was a suspicious smell of gas".

Interior Minister Gerald Darmanin visited the scene on Sunday and Housing Minister Olivier Klein is due to visit 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.

Christophe Mirmand, a local authority leader in the Bouches-du-Rhone region, said there was no danger notice on the building and that it was not in a neighbourhood identified as having substandard housing. The comments were echoed by Mr Payan. — BBC