A construction crane toppled across all lanes of the Tappan Zee Bridge on Tuesday, snarling traffic but causing only minor injuries in an incident Gov. Andrew M. Cuomo called “nothing short of a miracle.”

Four people — a construction worker and three others in vehicles — suffered minor injuries in the noontime incident, during which the boom of a crane operating a vibratory hammer crashed across the bridge, which spans the Hudson River between Rockland and Westchester counties north of New York City.

The drivers got into “fender-benders” while trying to avoid the crane debris, Cuomo said.

The worker was taken to Nyack Hospital for treatment of a minor shoulder injury after he dove for cover while working on a cofferdam — a platform below the bridge, said Kieran O’Leary, public information officer for Westchester County police. Cuomo’s office said the crane operator was not among the injured.

“Given the accident and given what it could have been, I’m going to say a special prayer, because this was nothing short of a miracle,” Cuomo said at a news conference in Tarrytown on Tuesday. “We were very, very lucky this is the consequence of what could have been a really, really terrible tragedy today.”

A team of structural engineers flown in to the site Tuesday inspected the bridge for both visible and unseen damage, Cuomo said.

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The inspection found the debris caused “significant” damage to one southbound lane of the bridge, and Cuomo said authorities were still determining what happened to cause the crane failure.

“We don’t know exactly what caused the malfunction,” he said.

The crane was one of 28 working on the bridge project, in which the Tappan Zee is being replaced by a new span, he said.

“Dozens and dozens of cranes have been operating on that bridge for months,” Cuomo said. “This is the first accident we’ve had. We don’t know what caused the accident at this crane. If there’s a silver lining to this, it would be that no one was seriously hurt.”

Terry Towle, president of Tappan Zee Constructors, the project’s design-builder, said at the news conference that the crane was new and that wind did not play a factor in its failure.

“Obviously, it’s one of three issues: It’s a problem with the crane; it’s a problem with the hammer; it’s operator error,” he said. “That’s what the investigation will look at.”

Cuomo said the other cranes at the bridge also would be inspected.

We want “to make sure this never happens again, that’s what we want,” he said.

The crane was driving pilings into the riverbed — “a routine task, not a special task,” Towle said. A representative of the crane’s manufacturer had been at the scene at the time of the collapse, Towle said.

The incident kept vehicles stalled on the bridge and its arteries for hours. While traffic largely had resumed by the evening rush hour, Cuomo advised motorists to consider alternate routes.

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Atabey Sanchez-Haiman, 35, from Providence, who was nearly across the bridge when the crane collapsed, described a scene of motorists idling in their vehicles, waiting for information after the incident.

“Many came out of their cars to walk their dogs and talk to others, and some were looking for a bathroom,” Sanchez-Haiman said. “A few people walked to the end to see what was happening and came back to report to the rest of us.”

Taylor Neill, 17, of Southampton, was en route to Nyack to visit her aunt when her family’s car became stuck on the bridge due to the collapse.

“There were a lot of people . . . trying to make the best of the situation,” Neill said. “Many were getting out of their cars and taking photographs. Some were even playing football.”

Several South Nyack residents took a stroll, some with their dogs, on an overpass above I-287 near the foot of the bridge to get a look at the accident. Most were taking photos of the wreck with their smartphones, in awe of what they saw.

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Melissa Salemo, a human resources employee in Westchester, said she left work about an hour after the crane collapsed to pick up her son at baseball camp in Rockland.

Knowing about the closures, Salemo planned ahead and traveled north to the Bear Mountain Bridge, which was teeming with rerouted traffic.

“It took me about two and a half hours for a trip that would normally be about 30 minutes,” Salemo said. But, she added, the important thing was that few were hurt.

“It could have been a lot worse,” she said. “Thank God for that.”

It was the second major incident associated with the bridge replacement project this year. In March, a tugboat collided with a construction barge moored under the bridge and sank, killing all three of the tugboat’s crew members, including a man from Westbury.

Three years ago, a Nyack man who was boating while intoxicated crashed his vessel into a construction barge at the bridge, killing two of his passengers.

With Danielle Ohl and Sarah Armaghan