NEW YORK - A construction crane snapped and smashed into an apartment building with a thunderous roar yesterday, killing two workers in the city's second such tragedy in 21/2 months and renewing fears about hundreds of cranes in the city.

The collapse happened despite stepped-up inspections and a shake-up in the city Buildings Department after the earlier accident, which killed seven in March.

The collapse on Manhattan's Upper East Side occurred just after 8 a.m. at the site of a 32-story tower that is to house a public school and apartments. Witnesses said the boom - the long arm that hoists materials onto the building's newly laid concrete slabs - snapped off its turntable, the platterlike platform that holds the cab for the operator. Then, witnesses said, the cab and the boom flopped to one side.

They went into free fall, slamming a corner of a 23-story building across the street, shearing off balconies and leaving a trail of pockmarks as they clattered to the street.

"It was like an earthquake," said Tara Hamilton, who lives nearby. "It was really bad, and it felt terrible. I didn't know where to run. I knew it was the crane."

Investigators were looking at whether a bad weld had caused the top of the crane to snap, a city official said, and whether the turntable was one that had recently been repaired after developing a bad crack.

Mayor Michael Bloomberg earlier called the accident "unacceptable and intolerable" but added: "Having said that, we do not know at the moment what happened or why."

With the city going through a building boom, about 250 cranes were in operation as of mid-March. Nine people have died in crane accidents this year. None died last year; two were killed in 2006.

"How many people have to die before the mayor decides enough is enough?" Councilman Tony Avella asked.

Councilwoman Jessica Lappin, who represented the neighborhood affected by the March collapse, said: "People shouldn't live in fear walking near a construction site - and certainly shouldn't feel fear sitting in their living rooms."

City records showed officials halted work at the site of yesterday's accident after the crane failed a "load test" April 22. The crane passed a second test the next day; no violation was issued.

Records also indicate several neighborhood complaints about cranes at the site in recent weeks.

Inspectors found most of the concerns were unwarranted, and Building Department officials said the crane had been inspected frequently.

The operator of the crane, Donald Leo, 30, of Staten Island, was sitting in the cab as the structure fell. He was pulled from the wreckage by rescuers and pronounced dead at the scene. A second man, Ramadan Kurtaj, 27, of the Bronx, was also killed.

No one in the building was hurt, and one pedestrian was treated for a minor injury and released, the mayor said.

Construction foreman Scott Bair said one worker on his 40-man crew was taken to the hospital with his "chest slashed open." His eyes filled with tears, Bair said his own life was saved because he left to get an egg sandwich just before the collapse.

Caitlin Reeves, 25, who lives in a corner apartment on the 10th floor of the damaged building, said she was brushing her teeth when she felt and heard an enormous rumble through her apartment - the effects of the broken crane shearing off her balcony.

"I turned around and ran into my room," she said, "and there were pieces of the wall and debris everywhere."

This article contains information from the New York Times.