NEW YORK — A crane rising 19 stories alongside a skyscraper under construction toppled like a tree across a city block Saturday, crashing into apartment buildings, killing four people and setting off a scramble for survivors.

The crane split into pieces as it fell, pulverizing a four-story townhouse and demolishing parts of three other buildings. One man was pulled from the townhouse 3 1/2 hours after the building was crushed.

Mayor Michael Bloomberg said at least four people, believed to be construction workers, have died and at least 10 people were injured in one of the city's worst construction accidents in recent memory.

The collapse devastated the affluent block on Manhattan's East Side: Cars were overturned and crushed. A huge dust cloud rose over the neighborhood. Rubble was piled several stories high.

"It's a horrible situation, very gory. There's blood in the street," said Lt. Gov. David Paterson, who takes over as governor for disgraced Eliot Spitzer on Monday.

An intensive rescue operation was under way to find anyone possibly trapped in the rubble on 51st Street near 2nd Avenue.

Fire Commissioner Nicholas Scoppetta said the rescue was "a painstaking hand operation, as we try to remove the rubble so we don't cause further collapse or injure anyone who may still be in that building." He said the operation would continue all night if necessary, including the use of search dogs and thermal-imaging and listening devices.

John LaGreco, who owned a tavern called Fubar that was closed when the brownstone was crushed, said his employee, Juan Perez, was the man pulled from the rubble. He said Perez suffered a broken leg. All of his employees were accounted for.

"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."

About 19 of the planned 43-story condominium had been erected, and the crane was scheduled to be extended Saturday so workers could start work on a fresh story, said an owner of the company that manages the construction site.

A piece of steel fell and sheared off one of the ties holding it to the building, causing it to detach and topple, said Stephen Kaplan, an owner of the Reliance Construction Group.

"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."

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's owner, New York Crane & Equipment Corp., were not immediately returned.

Kaplan wasn't sure whether any workers at the site were among those killed.

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, extending prayers to the families of the dead and injured.

Neighborhood residents said they had complained to the city several times about the construction at the site, saying crews worked illegal hours and the building was going up too fast.

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.

City Building Department records showed that on March 4, a caller told officials 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.

The collapse comes amid a building boom in New York City and follows a spate of construction accidents in recent months, including some involving cranes.

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.

At a Donald Trump hotel-condominium tower, a worker plummeted 40 stories to his death last month when a concrete form gave way. A month before that, a crane's nylon sling broke away and dropped seven tons of steel onto a construction trailer across from ground zero, injuring an architect.

On Saturday, nearby residents reported hearing a terrible roar as the structure detached from the condominium.

"First I heard a rumble, and it increased, and then it increased," said Bill Reilly, who lives a block away. "It continued building in strength until there was a final vroom!"

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Associated Press Writer Verena Dobnik contributed to this report.

(This version CORRECTS that East 51st Development Company owns the property).)