Oakland, California (CNN) At least 33 people have been confirmed dead, including teenagers and a deputy's son, in a massive blaze that gutted a converted warehouse over the weekend during an electronic dance party.

The death toll is expected to rise as crews search the wreckage of the two-story building, which burst into flames late Friday night. Roughly 30% of the building had been searched as of Sunday afternoon, Alameda County Sheriff's Sgt. Ray Kelly said in a news conference Sunday.

By Dan Simon, Max Blau and Eliott C. McLaughlin, CNN

It could take weeks to identify victims through DNA and dental records, he said. Officials have asked victims' families to preserve potential DNA samples from such items as their loved ones' hairbrushes and toothbrushes to assist in identifications. He added that officials were also working with the transgender community to identify some of the victims.

The City of Oakland identified the first eight victims Sunday night. One is a 17-year-old minor whose name will not be released, the city said. The rest have been identified as Cash Askew, 22, David Clines, 35, Donna Kellogg, 32, Travis Hough, 35, all of Oakland; Nick Gomez-Hall, 25, of Coronado, California; Sara Hoda, 30, of Walnut Creek, California; and Brandon Chase Wittenauer, 32, of Hayward, California.

"The scope of this tragedy is tremendous," Oakland Mayor Libby Schaaf said Sunday. A criminal investigation team is on the scene as a preliminary measure, she added.

The recovery search would be long and arduous as firefighters work to remove debris "literally bucket by bucket in a methodical, thoughtful, mindful and compassionate way," Oakland battalion Fire Chief Melinda Drayton said.

"We had firefighters with basically coveralls and buckets and shovels taking bits of debris out into the vacant lot to be loaded into dump trucks and removed to an off-site location," she said.

Drayton, who has been with the department for 19 years, called it one of the most deadly fires in the city's history. A fire in Oakland Hills in 1991 killed 25 people.

Even after firefighters put out the blaze Saturday, the building was deemed too unsafe for emergency responders to enter. Officials say the roof collapsed onto the second floor and then parts of that collapsed on to the first floor.

A former California state chief fire marshal said firefighters have to move slowly and cautiously for several reasons.

"One is falling debris," James McMullen told CNN Sunday. "One is building collapse. One is the fact that you don't want to disturb evidence that's critical for the fire investigation. ... So the key thing is, you've got to move slowly and you've got to preserve the scene at the same time so that the fire investigators can in fact determine the area of origin and subsequently the point of origin (of the fire), and then determine the cause."

'You could feel the heat of the flames'

Freelance journalist Sam Lefebvre said many people were just arriving at the warehouse when the fire started, because the dance party was supposed to go very late. The warehouse is a "sort of live/work art space with a lot of old decorations and furniture," Lefebvre told CNN. An electronic music DJ known as Golden Donna was scheduled to perform.

By the time John Evanofski arrived at 31st Avenue, giant flames lit up the night sky amid the billows of black smoke.

"You could feel the heat of the flames," he said. "Most of us were crying or unable to react. It was so hot and so terrible knowing that so many of us were still inside."

A Facebook page created for the event became a forum for friends and family of the victims, who posted frantic messages seeking information about loved ones. Those who survived shared their names to show they were safe.

Before the fire, an undated photo from Google Earth shows the building at 1305 31st Ave. in Oakland.

'I had to let him go'

For filmmaker and photographer Bob Mulé, the warehouse was both his home and his community.

The 27-year-old Mulé said more than 20 people living in the warehouse paid rent and were all involved in the creation of the space.

On Friday night, Mule stopped upstairs to listen to some music he described as a "very tame setting." Afterward, he headed downstairs to work on a painting. From his studio, he smelled smoke.

After seeing the flames, Mulé ran to find a fire extinguisher. He found one, but could not open the pin. When Mulé turned back to save his camera and laptop, he spotted a fellow artist who called out for help. Mulé suspected that heavy-set artist had broken his ankle after falling from the second floor.

"I was pulling him out," said Mulé, who suffered burns from the fire. "The flames were too much. There was too much smoke and ... I had to let him go."

Photos: Oakland warehouse party fire A fire breaks out Friday night, December 2, during a party at a two-story warehouse and artists' studio in Oakland, California. Initial reports indicate dozens of people were in the building when the deadly blaze started, the Oakland fire chief says. Hide Caption 1 of 7 Photos: Oakland warehouse party fire The scene as firefighters battle the blaze from video footage by @Oaklandfirelive early Saturday, December 3. Hide Caption 2 of 7 Photos: Oakland warehouse party fire Firefighters begin to assess the scene of the warehouse fire on December 3. Hide Caption 3 of 7 Photos: Oakland warehouse party fire Firefighters have not been able to search the entire building, the fire chief says. Hide Caption 4 of 7 Photos: Oakland warehouse party fire Crew will remove debris and make sure the warehouse is safe for searching. Hide Caption 5 of 7 Photos: Oakland warehouse party fire Firefighters clear an entry to the smoldering warehouse. Hide Caption 6 of 7 Photos: Oakland warehouse party fire Officials will begin investigating to determine the cause of the fire. The Alameda County Sheriff's Coroner's Bureau and the Arson Task Force were called to the scene. Hide Caption 7 of 7

The Oakland 'Ghost Ship'

The interior of The Ghost Ship, the warehouse that caught fire on Friday, December 2.

Photos posted online show an interior cluttered with drums, keyboards, guitars, clocks, ornate beds, plush sofas, mirrored dressers, tables, benches and artifacts. Exotic lamps hang from the ceiling, and paintings adorn some of the walls.

The interior of "The Ghost Ship"

Darin Ranelletti, Oakland's interim director of planning and building, told reporters Saturday the city had only approved permits for the building to be used as a warehouse, not for residences. City officials also had not signed off on a special permit for the event, Ranelletti said. In addition, firefighters found no evidence of sprinklers in the warehouse.

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Last month the warehouse's owners had received notification of city code violations for hazardous trash and debris, property records show. Officials had not yet completed an investigation into a November complaint about an illegal interior building structure.

CNN has reached out to the property owners for comment.

Coping with a nightmare

More than 40 people gathered Saturday at the Chapel of the Chimes in Oakland for a vigil for victims. Organizers asked attendees to light a candle at the end of the service, saying flames caused pain and destruction "but tonight we light the flame for good and for peace."

Now as loved ones seek answers, photographer Mulé must wrestle with the reality of losing a friend and grapple with his memories of the horrific night.

"I tried to save my friend but I had to leave him," Mulé said.