Investigators are zeroing in on gusting winds as a possible cause of Friday’s construction crane collapse in lower Manhattan, which killed a stock trader, injured three others and damaged surrounding buildings.

With snow swirling and winds topping 20 mph, workers attempted to lower the rig’s 565-foot boom for safety about 8:30 a.m., officials said.

The operator of the mobile crawler crane — positioned since Jan. 30 alongside a historic TriBeCa building — was performing the lowering when the cab and boom apparently turned into the wind, said a source familiar with the investigation.

The massive boom suddenly crashed down on Worth Street, between West Broadway and Church Street.

Killed as he walked along Worth Street was David Wichs, 38, a computer stock trader who apparently was going to his job at Tower Research Capital LLC on nearby Broadway, police said.

A 45-year-old woman sustained a leg injury and cut to her head, and a 73-year-old man suffered a head cut, according to police. Both were taken to hospitals, where they were later listed in serious but stable condition. Mayor Bill de Blasio said a third person suffered more minor injuries.

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The intersection would have normally been filled with people during rush hour, but workers had stopped traffic and were directing pedestrians away in advance of the crane being secured.

“It was something of a miracle there wasn’t more impact, and thank God the impact on people wasn’t worse, because this is an area that normally would have had a lot of people around it,” de Blasio said at a news conference.

A number of vehicles on Worth Street were crushed by the boom, which became a mangled mass of red steel. The crane’s cab was upended, its tank-like tracks in the air.

Officials said the crane was being used to replace rooftop air conditioners and generators at the 425-foot-tall former Western Union Building at 60 Hudson St. The operation had required permits, and the crane itself was inspected by the city’s Department of Buildings as recently as Thursday morning, officials said.

“They had inspected the crane . . . and reviewed the work that was being done and had approved it,” de Blasio said.

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The crane, with a load capacity of 330 tons, is owned by Bay Crane Co. of Long Island City, Queens. A crew from Galasso Trucking and Rigging of Maspeth was operating it. Neither company returned calls for comment.

Armando Alonso of Manhattan said he was evacuated from his West Broadway office and saw a lifeless man laying on the street.

“People were screaming and crying. It was terrible,” Alonso said. “This poor man was probably walking to work when he got hit.”

Wichs, a native of Prague, Czech Republic, came to the United States as a teenager and graduated from Harvard University, said his sister-in-law, Lisa Guttman.

“He really created a life for himself. He literally took every opportunity he could find,” she told The Associated Press.

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Buildings Commissioner Rick Chandler said the parapets of two buildings on Worth Street, next to New York Law School, were damaged and in danger of collapse. To minimize disruption, the city planned to put up a sidewalk construction shed.

Officials didn’t think the damaged crane would be removed before Monday.

De Blasio promised a full investigation by the NYPD and Department of Buildings.

A city official said there was no indication of alcohol being a factor, and the crane operator volunteered to take a blood test. Officials said wind, mechanical failure and possible human error were all being examined.

Tom Barth, of Barth Crane Consultants in South Carolina, said in a telephone interview that he viewed a short video of the collapse and believed wind “very possibly” was a factor in the accident.

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De Blasio said the crane manufacturer required the boom to be secured when winds exceeded 20 mph and that the crane company set 25 mph as the standard — both below the 30 mph standard mandated by the city for all crane operations to cease operations.

The mayor said Friday’s accident was the first crane collapse in the city since 2008, when two fatal accidents prompted the city to tighten safety regulations. During superstorm Sandy in 2012, a boom on a crane in Midtown twisted.

With Maria Alvarez