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Craig Ruttle, Associated Press
New York City firefighters stand near the damaged facade of 261 Madison Ave. after a piece of mechanical equipment being lifted by a crane broke free and fell about 28 stories to the sidewalk below, Sunday, May 31, 2015, in New York. Ten people including two construction workers were injured, but none of the injuries was considered life-threatening.

NEW YORK — A piece of mechanical equipment being lifted by a crane at a Manhattan office building broke free Sunday morning and fell about 28 stories to the sidewalk below, causing minor injuries to 10 people, officials said.

Two of the injured were construction workers, while the others were pedestrians and occupants of passing cars, Mayor Bill de Blasio said. All were struck by falling debris.

Police said the call came in around 10:45 a.m. Officers who responded to the high-rise building in Midtown East found that the crane's payload had broken free as it was heading to the top of the building. It fell to the sidewalk, shearing the side of the building along the way. The building is wider at the base and narrows at the higher floors.

De Blasio, speaking to reporters on Madison Avenue a block from the accident, called it "obviously, a very serious incident."

"Thank God, this incident occurred at an hour of the day on a weekend when there were not too many people around," he said.

Buildings Department Commissioner Rick Chandler said it was typical for work to be done on weekends when equipment such as a massive crane is being used, and all the permits for the work involving the crane were "in place."

He also said there have been no complaints about the crane. "We think this device, in this preliminary stage, is in good state and we'll follow up with that," Chandler said.

Authorities said a full investigation is underway. Streets were closed in the surrounding area, and officials hoped to have them open again by Monday morning's rush hour.