"It is a tragic event," Bloomberg said, adding, "Our hearts go out to all the victims and their families."
The big, white crane stood at least 19 stories high and had been attached to the side of a half-built high rise. When it toppled from its base on the sidewalk, part of it landed on a four-story brownstone, and turned it into a pile of brick. At least five other buildings had parts of their walls and roofs smashed or torn away, the city Buildings Department said.
A delicate rescue operation was under way to find anyone still buried in the rubble. One man was trapped inside the collapsed brownstone for 3 1/2 hours before firefighters rescued him.
Fire Commissioner Nicholas Scoppetta said the hunt would continue all night if necessary, and crews would use search dogs, thermal-imaging cameras and listening devices.
He called the work "painstaking," and said rubble was being removed carefully, sometimes by hand, to prevent further collapse.
The 2:20 p.m. accident turned an affluent Manhattan neighborhood into a disaster area: Cars were overturned and crushed. A huge dust cloud rose over the neighborhood. Rubble was scattered along the streets and piled several stories high where the building went down.
Ben Galati, a 54-year-old doorman at a high-rise apartment tower across the street from the construction site, said he was in the basement when it happened, and ran for his life when he heard the structure smash into his building.
"I heard a rumble outside. I said, 'Let's get out of here!' And then the crane came down. A split second later, I heard an explosion," he said.
Residents who lived near the site, on 51st Street near 2nd Avenue, said they had complained repeatedly in recent months that the crane appeared precarious.
About 19 of the high-rise condominium building's 43 planned stories had been erected, and the crane was scheduled to be moved Saturday so workers could start work on a fresh story when a piece of steel fell and sheared off one of the ties holding it to the building, according to Stephen Kaplan, an owner of the Reliance Construction Group, which manages construction at the site.
"It was an absolute freak accident," Kaplan said. "All the piece of steel had to do was fall slightly left or right, and nothing would have happened."
John LaGreco, who owned a tavern called Fubar located in the crushed brownstone, said his employee, Juan Perez, was the man pulled from the rubble hours after the collapse. He said Perez suffered a broken leg, but that all of his employees were accounted for. The bar was closed at the time of the accident.
"Our bar is done," he said. "The crane crashed the whole building. If I wasn't watching a Yankees game, I would've come to work early and gotten killed."
The crane, owned by New York Crane & Equipment Corp., split into pieces as it fell. Part of it came to rest against an apartment tower immediately across the street, buckling its facade and smashing it upper floors. That building and others in the area were evacuated.
Another piece of the crane hit broke off and was flung across the block, landing on the building that contained Fubar and damaging cars parked on 50th Street.
Maureen Shea said she was on the phone lying on her bed when she saw the giant white crane heading straight for her windows, but it missed her building.
"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," said the 66-year-old retired banker.
Lt. Gov. David Paterson, who takes over as governor for disgraced Eliot Spitzer on Monday, praised firefighters for taking "great risks" as they navigated the twisted brick and steel of the ruins to search for victims.
"Although we lost four lives, there were Herculean efforts to save three others," said Paterson, in town to meet with senior staff members. "It's a horrible situation, very gory. There's blood in the street," he said.
City Building Department records showed that on March 4, a caller reported that the upper portions of the crane appeared to lack the proper number of safety ties attaching it to the building.
A city inspector visited the site and determined on March 6 that no violation was warranted.
Another call questioning the crane's safety was dismissed as unwarranted by another inspector in February.
Kaplan said the company had subcontracted the work to different companies and was not in charge of the crane. Phone messages and an e-mail left for the crane company were not immediately returned.
James Kennelly, the lead partner at East 51st Development Company, which owns the property, issued a written statement expressing the group's dismay over the accident.
"There are no words to describe the level of devastation we feel today as a result of this tragic event," he said. "Our heart and prayers are with the families of those who died in this horrible accident. We are also praying for a full recovery for the individuals who have been injured today."
City officials said they had issued 13 violations to the site in the last 27 months, a normal amount for a project of that size.
Inspectors examined the crane Friday and found nothing wrong with it. Because high winds were predicted during the weekend, a stop work order on concrete work was issued by the Buildings Department on the site because materials were found to be too close to the building's edge. The order did not apply to moving the crane, which was permitted.
The catastrophe comes amid a building boom in New York City and follows a spate of construction accidents in recent months, including some involving cranes, though none as massive.
Earlier this year, a crane's nylon sling broke away and dropped seven tons of steel onto a construction trailer across from ground zero, injuring an architect. Last month, a worker at a Donald Trump hotel-condominium tower in SoHo plummeted 40 stories to his death when a concrete form gave way.
New York Crane was involved in a 2006 mishap, in which a 13-foot piece of a crane mast that was being dismantled fell into the street and crushed a taxi cab.
--- Associated Press Writer Verena Dobnik contributed to this report.
