The Oakland, California, warehouse that had been cobbled into artist studios that went up in flames late Friday did not have a permit to be used as a living space, nor did it have a permit for entertainment.

At least nine people died in the structure known as The Ghost Ship, where a late-night electronic dance party was underway when the blaze erupted.

Officials said Saturday the death toll could reach 40 and that many of the victims are young people in their 20s and 30s.

Oakland Fire Chief Teresa Deloche-Reed said at least 25 people were unaccounted for in what authorities were calling the deadliest building fire in the city in recent memory.

Officials had yet to determine how the fire started in the extremely cluttered building that was not equipped with sprinklers.

Arson investigators were called to the scene.

"It appears that either you got out or you got trapped inside," said Alameda County Sheriff's Office spokesman Sergeant Ray Kelly.

It took 55 firefighters about four hours to bring the fire under control, Battalion Chief Lisa Baker told the local newspaper, the East Bay Times.

Deloche-Reed said authorities had not yet searched the entire structure, which she described as "huge." The roof of the building collapsed, she said, further complicating the search effort.

"Right now, there's limited access to the structure, but it's too unsafe. And not only that, there's a lot of heavy wood from when the roof came in that's going to have to be removed," she told reporters. "So it's going to take us a while to finish up the search."

Firefighters used chain saws and axes Saturday to cut through the debris of the cluttered building, which lacked a sprinkler system that would have helped contain the blaze.

According to officials, the building was home to about 50 people who lived in an artist's collective, and a Facebook page for the event showed that 176 people planned to attend the party.

Oakland Mayor Libby Schaaf said in a statement that the fire was "an immense tragedy."

California Governor Jerry Brown, who is a former Oakland mayor, issued a statement saying he and his wife "were saddened to learn" about the fire.