The red chopper, which is owned by tourism group Liberty, was carrying six people including the pilot when it crashed into the river near the upscale Upper East Side neighborhood shortly after 7:00 pm (2300 GMT) on Sunday.
"Five people are deceased," a New York Police Department spokesperson told AFP, saying the dead were all passengers on the helicopter.
Following the crash, "the pilot freed himself, the other five did not," Fire Commissioner Daniel Nigro told reporters during an earlier press conference.
"We are told the five people were all tied tightly in harnesses that had to be cut and removed," he said.
Liberty organizes aerial tours of America's financial capital. Police chief James O'Neill said the aircraft had been leased by photographers.
The cause of the accident was not immediately clear, but local media indicated the pilot had sent a distress signal that mentioned an engine problem shortly before the crash.
The National Transportation Safety Board is investigating the incident.
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