Firefighters stand next to a truck moving rubbles where a building collapsed in Marseille, southern France, on April 9, 2023. AFP
"Everything shook, you could see people running and there was smoke everywhere, the building fell onto the street," local grocer Aziz told AFP, asking that his family name not be used.
"We have to be prepared to have fatalities in this terrible tragedy," Marseille mayor Benoit Payan told journalists at the scene in the central La Plaine district, where over 100 firefighters were battling an hours-long blaze.
It is unclear how many people were inside the fallen block -- believed to have one apartment on each floor -- at the time of the collapse at around 12:40 am (2240 GMT).
Interior Minister Gerald Darmanin said on the scene that there were between four and ten people trapped under the rubble.
"We don't know if they're alive or dead," he told reporters, adding that authorities were also yet to discover the cause of the "very large blast" that prompted the collapse.
Five people were injured in neighbouring buildings which were damaged by the collapse.
The intense heat as the building burns has kept search dogs from picking through the rubble, with Darmanin saying it would be "several hours... maybe even longer" before the fire was out.
"Time is of the essence" to discover possible survivors among the ruins, Marseille fire chief Lionel Mathieu said.
Rescuers' task has been complicated by the partial collapse of one of the adjoining buildings, where eight people had to be brought down by ladder after taking refuge on a roof terrace.
Other buildings on the street were evacuated and their residents put up in schools, while an aid centre for people looking for missing family members or loved ones has been opened in a neighbouring district.
"I am thinking of those affected and of their loved ones... thank you to the firefighters and emergency workers," President Emmanuel Macron wrote on Twitter.
Cause of blast unclear
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".
"It sounded like an explosion," said Gilles, who lives near the fallen building, declining to provide his last name.
Eight were killed in Marseille in 2018 when two dilapidated buildings in the working-class district of Noailles caved in.
The accident cast a harsh light on the city's housing standards, with aid groups saying 40,000 people live in shoddy structures.
But authorities appeared to rule out structural issues in the latest collapse, in a neighbourhood known for its bars and nightlife.
"There was no danger notice for this building, and it is not in a neighbourhood identified as having substandard housing," said Mirmand.