Police say clutter made it difficult for people to escape
Thirty three bodies have been found in a fire-destroyed warehouse after a party in Oakland, California.
Announcing that the death toll had risen, Sergeant Ray Kelly, from the Alameda County Sheriff's Office, said crews has begun to get deeper into the building.
They were expecting to find more bodies as they advanced, he added.
Sergeant Kelly said earlier that the victims were believed to be people in their 20s.
The families of those feared dead have been asked to preserve DNA evidence, such as hair or tooth brushes.
A number of victims are said to be foreign nationals and embassies have been contacted.
Fire officials in Oakland fought back tears as they revealed details of the search at a news conference.
Oakland battalion fire chief Melinda Drayton said firefighters worked through the night in the gutted building.
They have gone through the building searching the debris, "bucket by bucket," Ms Drayton said.
"It was quiet, it was heartbreaking," she said. "This will be a long and arduous process."
Officials did not update the number of people who were not accounted for.
The blaze tore through the two-storey building at about 11.30pm on Friday during an event featuring electronic music act Golden Donna.
Police told local television station KTVU that the warehouse, known as the Oakland Ghost Ship, houses a group of artists and their studios.
Its website showed it to have a bohemian-type interior with a clutter of old sofas, pianos, turntables and statues.
Chief Deloach Reed said this clutter "made it difficult for people to escape".
Bob Mule, an artist who lives in the building and suffered minor burns, said: "It was too hot, too much smoke, I had to get out of there.
"I literally felt my skin peeling and my lungs being suffocated by smoke. I couldn't get the fire extinguisher to work."
A woman who used to live there, Shelley Mack, said there were "all kinds of electrical cords running through there illegally.
"Massive extension cords. Heavy musical equipment."
She added: "That place was just a death trap.
"I didn't think it was going to last this long before it went up or somebody shut it down."