OAKLAND, Calif. — California officials fear dozens may have died in a massive fire that swept through an Oakland warehouse where a rave concert was taking place Friday night.

Ten people have been confirmed dead, and dozens of others remain missing, officials said. Nine bodies were recovered Saturday. Officials confirmed the tenth victim was found Sunday morning, Fox affiliate KTVU reported.

In a news conference Saturday, authorities said they expected the death toll to rise, but they did not know by how much.

“We’re expecting the worst — maybe a couple dozen victims here,” Sgt. Ray Kelly, spokesman for the Alameda County Sheriff’s Office told reporters. “We did not have a lot of victims go to the hospital. It appears that people either made it out, or they didn’t make it out.”

Seung Lee and his friends left the concert, a party featuring musician Golden Donna’s 100% Silk West Coast Tour, to buy some drinks, Lee told the Los Angeles Times. When they were walking back, they saw black smoke coming out of the warehouse’s first floor while fire engulfed the back of the building.

“The hardest thing I’m having trouble processing are the people on the second floor,” Lee, 24, told the Times. “I saw them dancing and having a fun time, and 10 minutes later they were trapped in this inferno.”

The three-alarm fire was reported at about 11:30 p.m. Friday at the warehouse known as Oakland Ghost Ship on 31st Avenue, a short block off International Boulevard, one of the main thoroughfares of East Oakland’s Fruitvale neighborhood. Oakland Fire Chief Teresa Deloach-Reed told The Washington Post that more than 50 people were inside.

The concert was being held on a second floor, where most of the recovered bodies were later found. A makeshift stairway put together with pallets was separating it from the first floor, Deloach-Reed said.

By the time firefighters arrived at the scene, the staircase had burned away, Mark Hoffmann, deputy chief of the Oakland Fire Department, said Saturday.

The building’s instability slowed the recovery effort on Saturday. Officials said the building’s roof had collapsed onto the second floor and, in many areas, the first floor as well. Firefighters and structural engineers spent much of the day shoring up the structure so it would be safe to enter the building and recover the bodies. Hoffman told Reuters about a dozen people survived the blaze, including one who went to a local hospital.

Drones equipped with thermal technology were used to scan the building for possible survivors, Kelly said. Initial reports, however, were grim.

“The drones were being used with a thermal imager,” Kelly said. “It’s very, very helpful technology. It allows us to focus in, and we can actually see the heat coming off of someone if they are alive. We didn’t see any heat signatures of live people. Not to say that there’s not, but the chances are very small.”

Authorities said it wasn’t clear whether electrical issues, pyrotechnics, or errant candles or cigarettes had started the fire. Fire officials said the building did not have sprinklers.

An arson investigation would also be underway, though the fire is not being investigated as a crime, Officer Johnna Watson, a spokeswoman for the Oakland Police Department, said.

As darkness fell here on Saturday, the scene around the warehouse had begun to stabilize. The burned building, with all of its windows blown out, had blue Alameda County Sheriff’s Office tents lined up on both sides of the entrance.

The city planning and building department had previously investigated the warehouse due to complaints about trash outside the property and illegal internal structures built inside the warehouse, said Darin Ranelletti, the department’s director. Complaints had been filed about the building as recently as November.

Ranelletti said authorities are still investigating whether people were living in the building. The last permitted use of the building was as a warehouse, so neither habitation nor a concert would have been legal without permits.

One survivor, Bob Mule, said he was one of 18 artists living in the warehouse, according to the Associated Press. In an interview with KGO-TV, Mule said he and another person saw the fire and started yelling. “The fire went up really, really, really quickly,” he said.

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. “It was a labyrinth,” said Hoffman.

Officials asked for patience and respect for the victims’ families as they investigate the many questions that remain, including the fire’s cause, the building’s history, and whether the party’s attendance exceeded its maximum occupancy.

At a news conference on Saturday, Oakland Mayor Libby Schaaf said she had met earlier that day with a “roomful” of people who were missing loved ones. “This is a devastating scene. This is complicated and it is going to take us time to do the methodical, thorough and professional investigation that these families deserve to find out what in fact happened,” she said.

The majority of those inside the building were young people, some of whom were from outside the Bay Area or the United States, Kelly told reporters.

A fire broke out at a warehouse in Oakland, Calif., where a concert was taking place on the night of Dec.2, killing at least nine people. (Oakland Fire Dept.)

The event’s Facebook page filled with inquiries on Saturday from people looking for their loved ones or offering their assistance to families and friends of the victims.

Friends and family members of the concert goers also cobbled together a list of missing people in a shared Google docs spreadsheet, along with identifying features and contact numbers. Forty names were listed on the spreadsheet as of Saturday evening; seven were marked either safe or in the hospital. The list is now private.

Deloach-Reed said fire officials will verify those names against the ones they have compiled.

“This is pretty tragic for us,” Deloach-Reed said. “It is hitting this community pretty hard. I don’t even want to talk about how the families and friends are feeling. We have a community that’s hurting.”

The building itself was considered to be an “artist collective,” as city officials put it, with spaces there for artists to work.

“It was beautiful,” Pete Veilleux, friend to several of the building’s residents and the owner of a nearby native plant nursery called East Bay Wilds, said. “It was like an art gallery, but people lived there.”

Veilleux was walking with his 10-year-old dog, Lucy, hoping to get updates on the status of the people he knew who lived there. He was relieved to learn that some of them had made it out all right, but still didn’t know what had happened to everyone.

He said he visited the space often, but never attended parties that were hosted there, like the one that took place Friday night.

Such parties are a common part of the Oakland community, which features an eclectic underground club and music scene.

Joel Shanahan, a Wisconsin-based electronic dance musician whose stage name is Golden Donna and who was headlining the concert, survived the fire, according to the artist’s Facebook page.

“Joel is safe but like many people he is heartbroken and has several friends among the missing,” according to a Facebook post.

Two organizations, the Oakland A’s and  Gray Area Foundation, set up online relief funds for the victims. Nearly 145,000 has been raised as of Sunday morning. A GoFundMe campaign has so far raised a little more than $4,000.

Saturday night, the Golden State Warriors held a moment of silence before their game at nearby Oracle Arena in the city to honor the victims of the fire. The team also pledged to donate $50,000 to support the families impacted by the fire to the Unity Council. The nonprofit helps low-income families in Oakland’s Fruitvale district.

A total of 72 firefighters responded to the fire, Deloach-Reed said. Crews had to fight the blaze from outside because it was too hot and intense for firefighters to go inside the building, she said.

Watson, of the Oakland Police Department, said investigators have talked to people who either left the building before the fire broke out, or were able to escape. She declined to share further details.

On Saturday, police had closed off a two-block radius on all sides of the building. First responders had turned the parking lot of the Wendy’s near the the warehouse into a command center.

Meanwhile, onlookers convened just outside the police tape to take in the scene. One man, who wasn’t willing to give his name, had been to multiple parties at the warehouse, which he said had been going on for the past five years.

“That party, the police didn’t know that party was there, because you can’t hear it from the outside,” the man said. “We used to have parties, underground parties, in all kinds of underground warehouses where no one would have died in a fire, and you would get out, no problem.”

At the corner of 31st Avenue and East 12th Street, passersby wove flowers – both individual ones and bouquets – into a chain-link fence surrounding a house about a hundred yards away from the warehouse.

Deloach-Reed said this is the worst fire the city has seen since the Oakland hills firestorm that killed 25 people in 1991. That fire, which rapidly spread through the Oakland hills wiped out nearly 3,500 homes, according to the San Francisco Chronicle.

City officials made it clear it will take time for a full investigation and search-and-rescue mission to be completed. Kelly said it would take “a minimum of 48 hours” to recover all the bodies within the structure.

News like that won’t be much comfort to people like Danetta Logan. A postal worker with a route starting on 69th Street, a few miles east of the warehouse, Logan was on the scene hoping to find a woman on her route, Mary Canteras, who she said had been alone and searching for her missing 14-year-old daughter since 4 a.m.

“I came here hoping to see her because she’s been out here by herself,” said Logan, who was in uniform.

“I talked to her, and she was out here, and her phone was going dead, so I’m sitting here hoping she calls back.”

While police couldn’t confirm there were any minors present at the party, there appeared to be at least one, which was what made Logan most upset about the entire tragedy.

“That’s the biggest problem with this,” he said. “Just a lot of babies that got let in.”

Bontemps reported from Oakland. Guerra and Swanson reported from Washington.