MARSEILLE, France >> Eight people remained missing after the building they lived in exploded and collapsed early Sunday near the port of Marseille, leaving mounds of burning debris hampering rescue operations, officials said.

More than 100 firefighters worked against a ticking clock to extinguish flames deep within the rubble of the five-story building, but more than 17 hours later “the situation is not yet stabilized,” Marseille Prosecutor Dominique Laurens said at an evening news conference.

Earlier in the day, officials had thought that between four and 10 people may have been trapped. Laurens said police have yet to confirm the apparent disappearance of a ninth person who lived in a next-door building. Five people suffered minor injuries from the collapse, which occurred shortly before 1 a.m.

Marseille Mayor Benoit Payan said two buildings that share walls with the one that collapsed were partially brought down before one later caved in, another complication in the search and rescue operation. The buildings were among evacuated structures.

Drones and probes have been used to examine the scene for signs of life. The burning debris was too hot for dogs in the firefighters’ canine team to work until Sunday afternoon, though smoke still bothered them, the prosecutor said.

“We cannot intervene in a very classic way,” Interior Minister Gerald Darmanin said during a morning visit to the site. He said the fire was burning a few meters under the mounds of debris and that both water and foam represent a danger to victims’ survival.

An investigation has been opened for involuntary injury, at least initially sidestepping possible criminal intentions. A gas explosion was among the tracks to check, said Laurens, the prosecutor. But the start of the probe also was limited by the heat of the blaze.

“The flames weren’t pink. They were blue,” Payan said.

Firefighters, with the help of urban rescue experts, worked through the night and all day Sunday in a slow race against time. The delicate operation aimed to keep firefighters safe, prevent further harm to people potentially trapped in the rubble and not compromise vulnerable buildings nearby, already partially collapsed. Some 30 buildings in the area were evacuated, Darmanin said.

Lauren, the prosecutor, said that firefighters “are really in a complicated situation, dangerous for them.” Work is progressing but with safety precautions, she said.

“We heard an explosion … a very strong explosion which made us jump, and that’s it,” said Marie Ciret, who was among those evacuated. “We looked outside the window at what was happening. We saw smoke, stones, and people running.”

The building that collapsed is located on a narrow street less than a kilometer (a half-mile) from Marseille’s iconic old port, adding to an array of difficulties for firefighters and rescue workers. The prosecutor said the building and those next door “are not at all substandard buildings.”

Robots were reportedly being deployed. A crane was brought in to clear rubble and firefighters were at one point seen in TV video hosing parts of the debris from a window in a nearby apartment as plumes of smoke rose skyward.

“We’re trying to drown the fire while preserving the lives of eventual victims under the rubble,” Lionel Mathieu, commander of the Marseille fire brigade, said during a televised briefing.

“Firefighters are gauging minute by minute the best way to put out the fire,” Payan, the mayor, said.

“We must prepare ourselves to have victims,” he said grimly.

The collapsed building is located in an old quarter in the center of France’s second-largest city. The noise from the explosion resounded in other neighborhoods. Nearby streets were blocked off.

French President Emmanuel Macron and Prime Minister Elisabeth Borne both tweeted their thoughts for people affected and thanks to the firefighters.

In 2018, two buildings in the center of Marseille collapsed, killing eight people. Those buildings were poorly maintained — not the case with the building that collapsed Sunday after an explosion, the interior minister said.