The death toll from a massive weekend fire at a warehouse near San Francisco shot up to 36 on Monday as authorities launched a criminal probe and pushed forth with recovery efforts.

Of the 36 victims found so far in the wrecked two-story building that had been converted into an artists collective, 33 have been identified, authorities said.

Three of the deceased are foreign nationals from Finland, Guatemala and South Korea, Alameda County Sheriff Gregory Ahern said.

Most of the casualties at the so-called Ghost Ship building were in their 20s and 30s, and one was a 17-year-old boy.

Among the victims identified was a music therapist, a musician and a teacher, local media reported.

READ: Musicians, student among first list of Oakland fire victims

Alameda County District Attorney Nancy O'Malley told reporters that her office had launched an investigation into the blaze to determine whether there is criminal liability and against whom.

"The range of charges could be murder all the way to involuntary manslaughter," she said, adding that the probe could take weeks.

Officials said they expected to recover more remains from the warehouse in Oakland that went up in flames late Friday, trapping dozens of partygoers attending a rave.

But they said they did not expect the death toll to rise significantly.

Firefighters were forced to suspend their search late Sunday for safety reasons, but were able to resume their work early Monday.

"We're no closer to finding a cause and we absolutely believe that the number of fire fatalities will increase," Fire Chief Teresa Deloach Reed said earlier.

Officials warned the recovery work would drag on as firefighters were removing debris "bucket by bucket," moving it to an off-site location to sift through it.

By Monday afternoon, 75 percent of the debris had been removed, officials said.

President Barack Obama expressed sadness over the tragedy, the deadliest in California's modern history.

"While we still don't know the full toll of this disaster, we do know that an American community has been devastated, and many people -- including young men and women with their whole futures ahead of them -- have tragically lost their lives," he said in a statement.

The fire erupted in the back of the warehouse occupied by an arts collective as it hosted a dance party attended by between 50 and 100 people.

It spread quickly through the structure, trapping partygoers whose bodies were found scattered throughout the building's mazelike interior.

Power was cut off in the area for up to 12 hours from midday on Monday to allow crews to bring in a crane to help with cleanup efforts, police spokeswoman Johnna Watson said.

- Fast-moving blaze -

Survivors have spoken of the speed with which the fire spread through the warehouse with people banging on windows when they couldn't escape.

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!'"

In a macabre indication of what the fire may have done to the bodies, the authorities are asking relatives to preserve hairbrushes and toothbrushes to assist in matching DNA samples.

City officials acknowledged over the weekend that they had received a number of complaints about the warehouse and that inspectors had been there last month but left when no one answered.

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 minutes.

There were also questions about whether the building was properly equipped with sprinklers or smoke detectors.

Officials said the roof collapsed onto the second floor, which was connected to the ground floor only by a makeshift stairway made of wooden pallets and plywood.

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.