Authorities in Oakland, Calif., say dozens of people have died in a fire that broke out during a party at warehouse that served as an art and music venue. (Claritza Jimenez,Victoria Walker/The Washington Post)

OAKLAND, Calif. — The warehouse where at least 36 people died in a massive fire Friday night has been deemed too unsafe and unstable for emergency workers, prompting fire officials to temporarily halt search efforts that have now stretched into a fourth day.

Melinda Drayton, battalion chief for the Oakland Fire Department, said at a news conference Monday morning that crews stopped searching overnight after noticing that a wall at the back of the building was leaning at an alarming angle. The search was halted just after midnight, Drayton said, adding that once it resumes, “we absolutely believe that the number of fatalities will increase.”

Officials now believe that the deadly fire started at the back of the warehouse. But Drayton said Monday that significant investigative work is still ahead. “We are no closer to finding a cause,” she said.

The new death toll makes Friday night’s fire one of the deadliest in recent U.S. history — and the deadliest in Oakland since 1991. Firefighters worked nonstop over the weekend, searching through debris and rubble to recover bodies, many of which have been charred beyond recognition. Eleven of the 36 victims have been positively identified, officials said Monday.

Drayton said crews have searched about 70 percent of the building, a 10,000-square-foot warehouse that was converted into an artists collective and exhibition space and that has been investigated by city officials for blight and illegal structures. Structural engineers will be at the scene Monday morning, and officials hope to resume search efforts within four to six hours, Drayton said.

Firefighters work inside the burned warehouse following in the Fruitvale district of Oakland. (Lucy Nicholson/Reuters)

The massive fire that engulfed the building broke out late Friday night, during a concert attended by more than 50 people. Some of them are still missing. Others have been confirmed among the dead. On Sunday, the coroner’s office released the names of seven: Cash Askew, 22, David Cline, 24, Travis Hough, 35, and Donna Kellogg, 32, all of Oakland; Nick Gomez-Hall, 25, of Coronado, Calif.; Sara Hoda, 30, of Walnut Creek, Calif., and Brandon Chase Wittenauer, 32, of Hayward, Calif.

The youngest victim identified as of Sunday afternoon was 17 years old. That person’s name was not being released.

President Obama said his administration has made efforts to help local and state officials in the investigation.

“While we still don’t know the full toll of this disaster, we do know that an American community has been devastated, and many people — including young men and woman with their whole futures ahead of them — have tragically lost their lives,” Obama said in a statement Monday. Oakland, the president said, “is one of the most diverse and creative cities in our country, and as families and residents pull together in the wake of this awful tragedy, they will have the unwavering support of the American people.”

Visible police activity was subdued Monday morning after officials halted their search overnight due to unsafe building conditions. The smell of burnt debris no longer lingered, but the sidewalk in front of the building remained walled off by Alameda County Sheriff’s Office tents as rescue vehicles packed the neighboring Wendy’s parking lot.

Sol Rodriguez, center, and Aaron Torres visit a shrine for the victims. (Marcio Jose Sanchez/AP)

Lining the metal police barricades at a nearby intersection were flower bouquets, candles and a poster that read “We empower our people to heal our hearts.” A sparse crowd gathered near the police tape surrounding the area.

Locally known as Ghost Ship, the building is owned by Chor Ng and was leased to Derick Almena and his wife, Micah Allison. Almena started the artists collective, and he and Allison managed the space and allowed artists to live there for a small fee.

The building’s interior featured a tangled network of antique furniture, artwork, musical instruments, wooden lofts, tapestries and oddities, such as mannequin parts, according to a Tumblr blog that appears to show the building. A makeshift staircase made of wooden pallets led to a second floor.

By the time firefighters first arrived at the scene Friday, the second floor had burned down, and the building’s roof had collapsed.

The building’s instability hampered search efforts over the weekend, and the structure was initially deemed too unsafe for crews to go in. Firefighters moved slowly in the search, walking amid fallen beams and smoldering ruins as they looked for bodies. They undertook their mission at great risk, with ceilings and floors in danger of collapse. They doused flames by passing buckets down the line.

The firefighters ranged in experience from a few months to 30 years, but all were affected by the intensity of the blaze and the piles of bodies they encountered along the way, officials said.

“We had firefighters with basically coveralls and buckets and shovels, taking bits of debris out into the vacant lot, to be then loaded into dump trucks and removed to an off-site location,” Drayton said Sunday. “This will be a long and arduous process, but we want to make sure we are respecting the victims, their families and our firefighters’ safety to work slowly and carefully through the building.”

Drayton said majority of the victims were found in the middle of the building.

It remains unclear if the fire started on the first or second floor.

The fire began about 11:30 p.m. Friday, as partygoers gathered on the second floor to listen to a music group called Golden Donna. The band played before a dance floor of about 2,500 square feet. The music event’s Facebook page was quickly flooded with inquiries from people looking for their loved ones or offering their assistance to families and friends of the victims.

Questions remain about whether electrical issues, pyrotechnics or errant candles or cigarettes started the fire. Fire officials said the building did not have sprinklers. A criminal investigation team was sent to the site, officials said.

Officer Johnna Watson, spokeswoman for the Oakland Police Department, said that the answers won’t come anytime soon and that officials are more focused on keeping families informed. “They want to have answers,” she said. “We want to provide answers not only for the families, but for our community.”

The warehouse, on 31st Avenue near one of East Oakland’s main thoroughfares, had long been the subject of complaints. Local officials said they were alerted to possible code violations on Nov. 13, but they could not get inside the structure when they visited four days later. Local news outlets reported that a number of artists used the building as their sleeping quarters as well as studios.

Oakland Mayor Libby Schaaf said complaints as recent as November cited blight, trash and debris around the building, as well as illegal construction and residential use inside. An inspector who recently visited the warehouse documented the blight outside but was unable to go in. An investigation on possible illegal housing is pending.

Almena said his “heart is broken” over the deaths, according to NBC News. Efforts to reach Almena on Monday were unsuccessful. A number listed under his name was not accepting voicemails.

Shortly after the fire broke out, Almena wrote a Facebook post lamenting the loss of everything he’d worked for. He later clarified those comments.

“In my previous Facebook post, I had no idea there was loss of life,” he said in a statement to NBC News. “This tragic event consumes my every moment. My heart is broken. My heartfelt condolences to the family and friends who have suffered the loss of loved ones.”

He added: “My goal has been nothing less than to create an environment for art and creativity in our community. During this investigation please continue to show support and compassion for t hose affected by this tragedy. The prayers of my family and I go out to the families of the victims.”

Guerra and Kranish reported from Washington.