OAKLAND: The death toll from a blaze that gutted a warehouse during a rave party in Oakland, California has climbed to 24 and is expected to rise, police said Sunday.

"Thus far, with about 20 percent 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 previously said that nine people had died in the fire of undetermined origin that broke out late Friday in the city near San Francisco.

Up to now only three families of people missing in the blaze had 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.

"It will take a few more days just getting through the building," Drayton told reporters.

A dozen bodies were found in an area in the middle of the building, she said, explaining that the firefighters had taken every precaution to treat the human remains with respect.

Describing the atmosphere during the night of excavation, Drayton choked back tears: "It was quiet. It was heartbreaking."