The death toll in a fire that devastated a California loft building during a weekend dance party has climbed to 30 people and will likely rise further as recovery teams push deeper into the charred ruin, authorities say.

Oakland firefighters found the remains of 30 victims as they sifted through the debris-filled shell of the two-story converted warehouse in Oakland being used by an artists’ collective. The cause of the fire was still undetermined, officials said. Authorities said they did not suspect arson, but investigators want to find out if the building had a history of code violations.

“That is an astronomical number,” Sergeant Ray Kelly, a spokesman for the Alameda County Sheriff’s Office, said as he announced the number of fatalities. “We’re still not done.”

A charred wall is seen outside a warehouse after the fire broke out. (Photo: Reuters)

The blaze, which erupted about 11:30pm (local time) on Friday, already ranks as the deadliest in the United States since 100 people perished in a 2003 Rhode Island nightclub fire.

Chris Nechodom, 30, said he arrived early at the party, which featured electronic dance music, and was on the ground floor when he saw flames race across the ceiling. As he left he heard a loud noise and saw a huge plume of thick black smoke billowing out.

“It blew out maybe 10 feet out of the entrance. After that I saw a few more people crawl out,” he said.

Nechodom was surprised the number of victims was so high, given the relatively small size of the gathering. “It sounds like more people got stuck than got out,” he said.

He said he was unsure how many people were inside when the fire started. Many of the victims were believed to be in their 20s and 30s.

Firefighters carry equipment at the scene of the fire. (Photo: Reuters)

Family members were asked to preserve items that might contain DNA of the victims, including combs, toothbrushes and hair brushes, to help with identification.

“It’s a terrible thing to have to say that and to have to come out here and do that, but that is what we’re left to deal with here,” Kelly said.

As of Sunday morning, only 20 percent of the building had been searched, said Melinda Drayton, battalion chief at the Oakland Fire Department.

The recovery operation was delayed for hours as the roof collapsed onto the second floor and in some spots, the second story had fallen onto the first, making it unsafe to enter.

Firefighters have gone through the building searching the debris “bucket by bucket,” Drayton said.

“It was quiet, it was heartbreaking,” she said, referring to the search. “This will be a long and arduous process.”

Exhaustion and the scope of the disaster were taking an emotional toll on crews, officials said.

– Reuters