Rescuers with sniffer dogs and heat-sensing cameras are searching rubble in New York for survivors and victims of a crane collapse.
Four construction workers were killed when the giant crane toppled in Manhattan's affluent East Side.
At least 17 were injured in what Mayor Michael Bloomberg called one of the city's worst construction accidents.
It destroyed a four-storey townhouse and demolished parts of five other buildings.
On Sunday construction crews positioned a second crane to help remove pieces of the toppled crane, and begin removing piles of bricks and debris from the street.
Fire Commissioner Nicholas Scoppetta said rubble was being painstakingly removed, sometimes by hand, to prevent further collapses.
The crane, which stood 19 storeys high, was being used in the construction of a new high-rise apartment building.
Saturday afternoon's accident happened during an attempt to extend the crane to allow workers to start work on a new level of the building, said one of the owners of the company managing the construction site.
Stephen Kaplan, of the Reliance Construction Group, said a piece of steel had fallen and cut one of the ties holding the crane to the building, causing it to detach itself and fall.
"It was an absolute freak accident," he said. "All the piece of steel had to do was fall slightly left or right, and nothing would have happened."
He added that his company had sub-contracted the work to different companies, and was not in charge of the crane.
Reliance released a statement expressing sympathy for the families of the dead and injured.
It added that it had launched its own investigation, and was co-operating with external investigators.
The East 51st Development Company, which owns the property, also issued a statement expressing sympathy for the victims.
Eight people remain in hospital, including three in a critical condition, according to fire department officials. Nine others were treated at the scene, including five firefighters, they said.
Residents of the devastated townhouse said they were relieved that the accident had happened at the weekend, when fewer people were in the area.
John LaGreco, owner of the Fubar tavern on the building's ground floor, said an employee and a second person in the bar, which was closed, had been rescued.
"It's unbelievable that this happened," the Associated Press news agency quoted him as saying. "We're going to sue the hell out of them, of course."
Residents of the area reported hearing a loud roar as the crane came down.
"First I heard a rumble, and it increased, and then it increased," said Bill Reilly, who lives nearby. "It continued building in strength... it shook the six-storey brick building that I live in."
Maureen Shea, who lives opposite the under-construction building from which the crane fell, said: "I heard a big crash, and I saw dust immediately. Bricks were flying through the air.
"I saw the whole thing. I thought the crane was coming in my window."
The crane missed her building.