Firefighters are struggling to reach bodies trapped in the rubble of a converted warehouse ravaged by a blaze which tore through a late-night electronic music party.
The ferocity of the blaze at the warehouse in Oakland, California, has made the charred structure unsafe for emergency crews to enter. Nine bodies have been recovered but officials fear as many as 40 could be dead.
They described the scene inside the warehouse, known as the "Oakland Ghost Ship", which had been converted illegally into artist studios, as a death trap that made it impossible for many partygoers to escape the Friday night fire.
A day later, the maze of debris and devastation was complicating efforts to extract the bodies.
"It was just a labyrinth of little areas. We knew people were in there, and we were trying to get them out. But it was just a labyrinth," Oakland deputy fire chief Mark Hoffmann said.
He said firefighters had to halt their search and rescue operation on Saturday afternoon for safety reasons and shore up the structure. The building's roof had collapsed into the second floor, which in places fell to the bottom floor.
Oakland officials said they had opened an investigation just last month into the warehouse after numerous complaints filed by neighbours who said rubbish was piling up outside the property and people were living in the building, which was designated as a warehouse, illegally.
Darin Ranelletti of the Oakland Planning Department, said the city opened an investigation on November 13 and an investigator went to the warehouse four days later, but could not get inside.
One survivor of the fire, Bob Mule, said he and 17 other artists lived inside the warehouse. Online records listed the building's owner as Nar Siu Chor. Efforts to reach her at other associated Oakland addresses were unsuccessful.
The warehouse's website showed pictures of a bohemian, loft-like interior made of wood and cluttered with rugs, old sofas and a garage-sale like collection of pianos, paintings, turntables, statues and other items.
The website included advertisements for various electronic music parties. Friday night's event featured musician Golden Donna's 100% Silk West Coast tour.
It is unclear what sparked the fire but officials said the clutter served as a tinderbox and there were no sprinklers inside.
"Something as simple as a cigarette could have started this," Sergeant Ray Kelly of Alameda County sheriff's department said. He said people either escaped from the building or died inside, where the only way down from the second storey was via a stairwell made entirely of wooden pallets.
About 50 to 100 people were believed to have been at the party when the fire started at around 11:30pm local time on Friday, officials said.
Oakland fire chief Teresa Deloach Reed said at least 25 people were unaccounted for, all believed to be in their 20s. Kelly said as many as 40 may have perished and the coroner is preparing for a "mass casualty event" that could include victims from other countries.