A large crane at a construction site on Manhattan’s East Side collapsed Saturday afternoon, killing at least four people and injuring more than 10, officials at the scene said.

“This construction accident is one of the worst the city has had,” Mayor Michael R. Bloomberg said in a news conference this afternoon. “Our hearts go out to all the victims and their families.”

The big, white tower crane, which looked to be about 20 stories tall, appeared to have toppled across a street and crashed into other nearby buildings. Mr. Bloomberg said the falling pieces of the crane demolished one building and damaged three others.

The accident happened at 303 East 51st Street, near Second Avenue about 2:20 p.m., the authorities said.

Image Emergency workers at the scene of a crane collapse at 51st Street and Second Avenue in Manhattan. Credit... Tina Fineberg for The New York Times

“The main place of carnage was either at the construction site  among probably all construction workers, and I’m still trying to verify that  and then in the small building where the top piece of the crane came crashing down and just basically flattened the four-story town house right down to a mass of rubble,” Mr. Bloomberg said.

The mayor also said that the crane had been inspected and that the appropriate permits had been in place.

Aides to the Manhattan borough president, Scott Stringer, said they had been told by the Office of Emergency Management that the building that was destroyed was at 305 East 50th Street.

Mayor Bloomberg said that the firefighters and police officers on the scene were continuing to look for survivors in the rubble and that dogs and listening devices would be brought in.

He also said another crane was standing by to remove the broken crane but that first efforts would be made to stabilize the site.

Image Credit... The New York Times

Lt. Gov. David A. Paterson, who will be sworn-in as governor on Monday, visited the site of the accident and was briefed on the situation. “This is going to be a very, very difficult recovery,” he said in a news conference. “The crane is still balanced on the building and to take that down is going to take a tremendous effort.”

He added that New York City was the best equipped city to deal with a calamity of this scope.

Several neighboring buildings were evacuated and a shelter for people who had been displaced was opened at 228 East 57th Street, near Second Avenue, the mayor said.

“This is an absolute disgrace,” Mr. Stringer said. “We need better inspection and more resources.”

He said there were open violations on the construction site for a 44-story condominium building that are “quite serious,” he said.

Ismael Garcia, who was working on the 15th floor of the building under construction, said that just before the crane collapsed, it was lifting material that apparently fell and struck a girder that connected the crane to the building.

“Out of the corner of my eye, I saw a piece falling,” he said.

There was a loud crash, and he rushed to the edge of the building to peer out over the street below. “I saw a guy laying on the roof there,” he said, looking down on a building below. “His head was under the debris.”

Image Firefighters carried stretchers at the scene of the accident. People were feared trapped beneath the wreckage. Credit... Chip East/Reuters

Stephen Kaplan, an owner of the Reliance Construction Group, which manages the condominium construction site told The Associated Press that the crane had been scheduled to be raised on Saturday so work could begin on higher stories of the building.

He said a piece of steel had fallen, shearing one of the ties holding the crane to the building. “It was an absolute freak accident,” Mr. Kaplan told The A.P. “All the piece of steel had to do was fall slightly left or right, and nothing would have happened.”

Mr. Kaplan said his company had subcontracted the work to different companies and was not in charge of the crane.

Bartle Bull, who has lived in the neighborhood for 30 years, said he was not surprised that the crane had fallen. “What I’ve seen for the last two months is reckless construction and lack of enforcement,” he said in a telephone interview. “We have said this crane is going to come down.”

Mr. Bull said he deliberately avoided walking along 51st Street “because this thing looks so dangerous.”