Officials have said 36 people are now confirmed dead from a fire at a warehouse party in Oakland, California, and have opened a criminal inquiry.
Eleven victims have already been identified, with the families of those still missing being asked to submit DNA samples to investigators.
Crews have suspended body-recovery work for several hours due to fears that a damaged wall may collapse.
Authorities expect the total death toll to rise after crews resume searching.
“We are no closer to finding a cause, and we absolutely believe that the number of fire-fatalities will increase,” said Oakland Fire Battalion Chief Melinda Drayton.
US President Barack Obama paid tribute, saying: “Oakland is one of the most diverse and creative cities in our country, and as families and residents pull together in the wake of this awful tragedy, they will have the unwavering support of the American people.”
Officials believe they have located the section of the building where the fire was started, but its cause is not yet known.
About 70% of the building has been searched already, Oakland Police tweeted on Monday morning, but investigators have not been able to access the site since late Sunday night.
The city of Oakland has started to release the names of those killed, but withheld the name of the youngest, a 17-year-old.
The Ghost Ship fire’s victims
Cash Askew, 22
David Clines, 24
Nick Gomez-Hall, 25
Sara Hoda, 30
Travis Hough, 35
Donna Kellogg, 32
Brandon Chase Wittenauer, 32
Most of the victims were located in the centre of the warehouse structure, police said.
“We have 36 families not only grieving for their lost ones, but also they want to have answers. And we as a city collectively are working to find those answers,” said Oakland police’s Johnna Watson.
It is thought between 50-100 people were inside the venue when the fire broke out late on Friday.
The blaze caused the roof to collapse on to the second floor, part of which then fell through to the ground floor.
The opening of a criminal investigation allows authorities to preserve evidence and see if there was any criminal responsibility, whether through arson or negligence.
The building, known as the Ghost Ship, was used to house artists in improvised studios but several reports say people were illegally living there too.
Neighbours had complained to the city about rubbish piling up on the street outside, and about the illegal tenants.
“That place was just a death trap,” former resident Shelley Mack told the Associated Press. “I didn’t think it was going to last this long before it went up or somebody shut it down.”
Families of loved ones are now being asked to gather things like toothbrushes and combs to aid with DNA identification.
Media in Oakland named Derick Ion Almena as the co-operator of the collective with his partner, Micah Allison.
A Facebook post by him lamenting the loss of his belongings but saying he was “blessed that my children and Micah were at a hotel safe and sound” drew a barrage of criticism online.