The grisly search for bodies in the charred remains of a California warehouse will enter its third day Monday, with relatives of the missing being asked to provide DNA samples to speed up identification.
Only half of the burned-out building has so far been examined, with the confirmed death toll at 33, and officials admitted Sunday they do not know how many more dead they will find.
"We're expecting the worst and hoping for the best in regards to how many more victims we find," Sergeant Ray Kelly of the Alameda County Sheriff's Department said.
He said the search effort is expected to last days, with between 50 and 100 people believed to have attended the rave at the warehouse, which was used by artists.
In a macabre indication of what the fire may have done to the bodies, authorities are asking relatives to preserve hairbrushes and toothbrushes to assist in matching DNA samples.
"We will ask for them as we need them," said Captain Melanie Ditzenberger of the sheriff's department coroner's bureau.
Survivors of the blaze in Oakland spoke Sunday of the speed with which Friday night's fire spread.
Photographer Chris Nechodom, who was at the dance party, said people first thought the smoke was coming from a fog machine.
"And then it got a little thicker," he said. "It all happened within seconds. We started seeing people running around, frantic and screaming 'fire'."
Although the cause of the fast-moving blaze remains under investigation, Oakland Mayor Libby Schaaf said the district attorney had opened a criminal investigation as a precaution to preserve options as the case unfolds.
"You have to understand that the scope of this tragedy is tremendous," she said. "We have many, many witnesses to interview. We are in the process of doing that."
Eight victims have been identified based on fingerprints so far, ranging in age from 17 to 35.
Some were from Europe and Asia, and the Oakland authorities are working with the State Department to contact foreign governments, Kelly said, declining to reveal which countries.
Bodies were found scattered throughout the warehouse, known locally as Oakland Ghost Ship.
"We're finding people throughout the entire square footage of that structure," Kelly said. "It's so random. We're finding victims where we least expect it."
Oakland Fire Chief Teresa Deloach Reed has said the interior of the warehouse was maze-like, "filled end-to-end with furniture, whatnot, collections."
"There wasn't a real entry or exit path," she said.
Images published online show artwork, pianos and wooden objects throughout the building, which helps explain why the blaze raced through the structure despite firefighters' arrival within three minutes.
Firefighters also said the building appeared to have had no sprinklers or smoke detectors.
Officials said the roof collapsed onto the second floor, which was connected to the ground floor only by a makeshift system of wooden pallets.
A dozen bodies were found in an area in the middle of the building, Oakland Fire Battalion Chief Melinda Drayton said, describing how debris was being removed bucket by bucket.
The deadliest nightclub fire in the United States in recent decades occurred in 2003, when pyrotechnic effects by the rock band Great White set off an inferno at The Station nightclub in Rhode Island, killing 100 people.