Updated 8.17pm

Rescue workers on Monday recovered another two bodies from the rubble of a collapsed building in France's Marseille, bringing the confirmed death toll to five, with another three people still missing.

More than 24 hours after an explosion at the building, where residents reported a strong smell of gas, dozens of civil defence staff and sniffer dogs were working through the debris, where a fire still smouldered.

Housing Minister Olivier Klein said at the scene earlier Monday that four bodies had been found. But a few hours later, the emergency services announced that rescue workers had found the body of a fifth victim.

The deputy mayor of the Mediterranean port city, Yannick Ohanessian, had said rescue workers still hoped to find survivors.

The fire under the rubble has made it hard for the dogs to detect more victims or survivors.

Firefighter Adrien Schaller, who arrived on site at around 1:00 am on Monday (2300 GMT Sunday), described painstaking work to maximise chances of finding survivors.

"The heart of the blaze is deep underneath and hard to reach with the hoses. And we can't spray too much water to avoid creating a sort of mud," he said.

- 'Race against the clock' -Rescue workers were clearing away most of the rubble with an excavator, he said, stopping as soon as they spotted an air pocket to continue the work by hand.

"It's a race against the clock," he said.

Earlier Sunday, before the discovery of the bodies, local prosecutor Dominique Laurens had told reporters that eight people "were not responding to phone calls".

Five people in a neighbouring building sustained minor injuries in the blast and collapse, which occurred around 12:40 am on Sunday.

While the cause of the explosion is still to be determined, several residents have reported a strong smell of gas.

Saveria Mosnier, who lives on a street near the site in the La Plaine neighbourhood, said she was sleeping when a "huge blast... shook the room". 

"I was shocked awake as if I had been dreaming," she told AFP.

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

Ohanessian said several witnesses had reported "a suspicious smell of gas".

'Afraid'

Two buildings next to the destroyed property were severely damaged, with one collapsing later in the day without injuring any rescuers.

Almost 200 residents were evacuated from surrounding buildings.

The city provided some emergency shelter, and the local community also sprang into action to help coordinate housing and aid for them.

"A lot of families in the neighbourhood are afraid," said Arnaud Dupleix, the president of a parents' association at the nearby Tivoli elementary school.

A ninth person living in a neighbouring building had also been feared missing, but has since been in touch with relatives, the prosecutor's office said.

In 2018, eight people were killed in Marseille when two dilapidated buildings in the working-class district of Noailles caved in.

That disaster cast a harsh light on the city's housing standards, with aid groups saying 40,000 people were living in shoddy structures. 

But authorities on Sunday appeared to rule out structural issues in the latest collapse.

"There was no danger notice for this building, and it is not in a neighbourhood identified as having substandard housing," said Christophe Mirmand, prefect of the Bouches-du-Rhone region.