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Five people were killed when a private helicopter with six people on board crashed into the East River in New York City on Sunday, authorities said.

Three people transported to area hospitals after the crash later died, New York Fire Department spokesman Jim Long said. Two others were pronounced dead at the scene of the incident.

The helicopter is hoisted by crane from the East River onto a barge on Monday. Mark Lennihan / AP

The pilot freed himself and was taken to a hospital in "OK" condition, New York City Fire Commissioner Daniel Nigro told reporters Sunday night. The pilot was later named 33-year-old Richard Vance.

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The cause of the crash, which occurred at about 7 p.m. north of Roosevelt Island between Queens and Manhattan, remained unclear.

The chopper, which was operated by Liberty Helicopters, was being used for a photo shoot, Police Commissioner James O'Neill said. A message left with the New York City-based company seeking comment was not immediately returned.

Video that captured the incident showed the chopper landing in the water with its rotor blades still spinning. Moments later, the aircraft had turned sideways.

Nigro described removing the passengers from the chopper as "one of the most difficult parts" of the search and rescue operation.

Everyone but the pilot was "tightly harnessed," he said. "These harnesses had to be cut and removed in order to get them off this helicopter, which was upside down at the time and completely submerged.”

That water was 50 feet deep, below 40 degrees and moving at 4 mph, he added.

"It took a while for the divers to get the people out," Nigro said.

CORRECTION (March 12, 2018, 3:40 p.m. ET): A previous version of this article misspelled the last name of the New York City fire commissioner. He is Daniel Nigro, not Nigron.