OAKLAND, California (CNN) -- At least 33 people have been confirmed dead 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. Only some 20% of the building had been searched as of Sunday morning, authorities said.
"We anticipate that the number of victims ... will increase, " said Alameda County Sheriff Sgt. Ray Kelly.
Names of some victims could be released Sunday, Kelly said.
Oakland battalion fire chief Melinda Drayton said 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."
"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. An Oakland Hills fire 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.
"There's limited access to the structure," Reed told CNN affiliate KRON-TV in San Francisco "It's too unsafe. And not only that, there's a lot of heavy wood from when the roof caved in that's going to have to be removed."
Oakland Mayor Libby Schaaf called the fire an "immense tragedy" and pledged to get a "full accounting" that could be shared with the public as quickly as possible.
'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 since 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 told CNN. "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.
'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 told CNN 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 sustained burns from the fire. "The flames were too much. There was too much smoke and ... I had to let him go."