OAKLAND, California (CNN) -- Oakland authorities have already deemed the fire at a warehouse turned arts space to be one of the city's deadliest blazes ever. But the death toll is expected to rise as investigators slowly comb through the wreckage of the two-story building, officials said.
At least 33 people have been confirmed dead, including teenagers and a deputy's son, in a massive blaze that last Friday gutted a converted warehouse during an electronic dance party.
But less than a third of the building had been searched as of Sunday afternoon, Alameda County Sheriff's Sgt. Ray Kelly said in a news conference.
It could take weeks to identify victims through DNA and dental records, he said. Officials have asked victims' families to preserve their loved ones' personal belongings including hairbrushes and toothbrushes that could contain DNA samples. Kelly added that officials were also working with the transgender community to identify some of the victims.
The city's district attorney has activated a team to launch a criminal investigation.
"The scope of this tragedy is tremendous," Oakland Mayor Libby Schaaf said Sunday.
One of deadliest fires ever in Oakland
The City of Oakland released the names of seven victims Sunday night. They were identified as Cash Askew, 22, David Cline, 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 name of an eighth victim, a 17-year-old minor, will not be released, the city said.
Oakland Battalion Fire Chief Melinda Drayton cautioned that the recovery search could be a long and arduous process as firefighters work to remove debris "literally bucket by bucket in a methodical, thoughtful, mindful and compassionate way,"
"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, a 19-year veteran, called it one of the deadliest fires in the city's history -- including a 1991 fire in Oakland Hills that killed 25 people.
Officials said the roof collapsed onto the second floor. After that happened, parts of the second floor collapsed on to the first floor. Even after firefighters extinguished the blaze Saturday, they quickly deemed the building so unsafe that emergency responders couldn't enter as a precautionary measure.
'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."
Concerned family and friends used social media to find loved ones and offer support.
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.
Over the weekend, more than 40 people gathered 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."
'I had to let him go'
For filmmaker and photographer Bob Mulé, the warehouse was both his home and his community.
Mulé, 27, said more than 20 people living in the warehouse paid rent and all helped in the creation of the space.
On Friday night, Mulé 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."
The Ghost Ship: A haven for artists in a gentrifying region
The building is known as the "Ghost Ship." To the artists who lived and worked there, the "Ghost Ship" was a coveted haven in the Bay Area's gentrifying landscape of skyrocketing rents and disappearing artist spaces.
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.
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.
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.
'One of those Catch-22 situations'
Josette Melchor, executive director of Gray Area Foundation for the Arts, told CNN that most people familiar with Ghost Ship knew it had issues, that it was not quite up to code. So it goes for many live-work warehouses, as they struggle to accommodate demand from artists for affordable spaces. Fear of losing a home or displacing others keeps some people from reporting possible violations, she said.
"It's one of those Catch-22 situations. A lot of us knew it was unsafe and it could have been fine had there been a smaller amount of people," she said. "But when you start having big parties it crosses the line."
CNN has reached out to the property owners for comment.