PARIS, April 10 (AFP) - Two bodies were found in the rubble of a building that collapsed in Marseille following a major explosion, French authorities said early Monday, as rescue workers scrambled to find at least six people still unaccounted for.

The discovery of the bodies came about 24 hours after the blast brought down the four-storey building in the Mediterranean port city.

Emergency workers had continued rescue operations through Sunday night into the early hours of Monday with the help of a crane and lights, but a persistent fire underneath the rubble hampered their work, making it difficult for firefighters to deploy sniffer dogs.

"Given the particular difficulties of intervention, the extraction (of the bodies from the site) will take time," the fire department said in a brief statement announcing the bodies had been found.

"The judicial authority will then proceed to identify" the victims, it added.

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

Five people from neighbouring buildings sustained minor injuries in the blast and collapse, which occurred around 12:40 am on Sunday (2240 GMT Saturday).

"Tonight, the pain and sorrow are great," said Marseille mayor Benoit Payan in a statement.

"All services of the city, as well as the state, are still at this very moment fully committed to continue the search," he added.

The cause of the explosion is still to be determined, but investigators are looking at the possibility it was the result of a gas leak.

More than 100 firefighters were battling the blaze in the ruins of the building, which was believed to have one apartment on each floor.

Multiple witnesses described the explosion to AFP.

"I was sleeping and there was this huge blast that really shook the room. I was shocked awake as if I had been dreaming," said Saveria Mosnier, who lives on a street near the site in the La Plaine neighbourhood.

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

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