Oakland, California, firefighters inspect a warehouse on December 3, 2016.
The death toll from a blaze that gutted a California warehouse during a rave party has climbed to 24 and is expected to rise, officials said Sunday.
"Thus far, with about 20 per cent of the building searched we have located 24 deceased victims of this fire," Sergeant Ray Kelly of the Alameda County Sheriff's Department told reporters.
Authorities have said they fear the death toll could climb to 40 as they search the remnants of the converted two-story warehouse located near San Francisco in the city of Oakland.
The building had been used by artists as a living and work space but had no license for such use, officials said, nor for the electronic dance party under way when the blaze broke out late Friday.
Authorities had previously said that nine people had died in the fire, whose cause is still unknown.
Only three families of people missing in the blaze have so far been notified of the death of a loved one due to the arduous identification process, Kelly said.
Firefighters worked for 12 hours by night to enter the building, which they carried out by breaching a wall then clearing their way into the interior, said Oakland Fire Chief Melinda Drayton.
'A Few More Days'"It will take a few more days just getting through the building," Drayton told reporters. Authorities estimated that 80 percent of the structure still remained unsearched.
Images published online show artwork, pianos and wooden objects occupying the building, which helps explain how the fire was able to spread so quickly.
"It was filled end-to-end with furniture, whatnot, collections," Fire Chief Teresa Deloach Reed said Saturday. "It was like a maze, almost."
"There wasn't a real entry or exit path," she said.
In addition, firefighters said the building seemed to have 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, Drayton said.
She added that the firefighters had taken every precaution to treat the human remains with respect.
'It Was Heartbreaking'Describing the atmosphere during the night of excavation, Drayton choked back tears: "It was quiet. It was heartbreaking."
Most of those who perished in the blaze, which started about 11:30 pm Friday (0730 GMT Saturday) were thought to have died on the upper floor of the warehouse known as the Oakland Ghost Ship, Reed said.
The electronic dance music party was attended by an estimated 50 to 100 people.
Some of the missing were believed to be from overseas, making identification of the victims -- thought to be in their 20s and 30s -- more difficult.
The fire was described as the deadliest incident in Oakland since the 1989 Loma Prieta earthquake in northern California, which killed 63 people.
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 about 100 people.
Oakland, a city of some 420,000, was once deemed a largely unsafe area but is now home to a more affluent population attracted by affordable rent and proximity to San Francisco.