All five passengers aboard a helicopter that crashed into Manhattan's East River Sunday night have died, authorities said.
The red Eurocopter AS350, which officials said was operated by Liberty Helicopters and had been privately chartered for a photo shoot, apparently had engine failure.
The pilot -- who repeatedly radioed "May day! May day! and reported "engine failure" -- was the sole survivor. He was identified as 33-year-old Richard Vance of Danbury, Connecticut, and was treated and released from New York Presbyterian Hospital.
Vance "freed himself" and was cut out of a harness by personnel on an FDNY boat, Fire Department of New York City Commissioner Daniel Nigro said. The passengers were "tightly harnessed" in the helicopter, which was submerged upside down.
A 14-member team from the National Transportation Safety Board was headed to the scene Monday morning to investigate the crash.
A bystander captured video of the helicopter's descent into the water. The footage shows the final seconds as the chopper's propellers strike the glassy river's surface, its engine sputtering.
The helicopter hit the water between East 86th and East 96th streets near Manhattan's Upper East Side around 7 p.m., local and federal authorities confirmed. After impact, the chopper floated a mile or two south before emergency crews could bring it to a halt, officials said.
The pilot was experiencing engine failure just before he lost control, sources said. Vance told authorities he believed the engine had failed.
Sources told ABC's "Good Morning America" that the passengers were harnessed in tightly because they wanted the doors open to shoot photos.
"The pilot knew what to do because he wears that harness everyday," said ABC News aviation expert Steve Ganyard. "But these poor civilians out for a nice Sunday flight encountered something that was very, very difficult to survive."
He said military pilots are usually trained in what's called a "helo dunker," in which pilots practice getting out of harnesses while submerged in water and flipped upside down.
It was not clear if the passengers had received any training on how to escape the harness in an emergency. Liberty Helicopters did not immediately return requests from ABC News for comment.
Eyewitness Arineh Nazarian was dining at a restaurant when she spotted the red helicopter diving into the water.
"We were ... having dessert and noticed a red helicopter going full speed toward the water," she told ABC station WABC. "It almost looked very surreal, and next thing we know it's approaching the water slowly and then it just completely crashed."
Afterward, Nazarian said members of the Coast Guard arrived in an attempt to help the helicopter passengers.
"We're just hoping they survived," she added.
Police and divers braved the 50-foot-deep river, which was about 40 degrees Fahrenheit and moving at a speed of 4 mph on Sunday night.
Two of those who died were pronounced dead at the scene, Nigro said.
"We're all still ... like really shaken up," another witness told ABC News. "There was a lot of screams. It was just really horrifying."
New York Police Department Commissioner James O'Neill said there were "dozens of calls" reporting the helicopter crash.
Soon after the helicopter went down, a series of dispatches captured in real-time over FDNY's scanners by Broadcastify.com broke down the initial emergency response.
"We got reports from NYPD that a helicopter is upside down in the water," a dispatcher stated.
Divers from both the NYPD and FDNY then raced into the water, according to the dispatcher.
O'Neill also praised the efforts of a private tugboat, which arrived on the scene before first responders.
"I want to thank the crew from the tugboat," O'Neill said. "They were the first boat on the scene."
He also confirmed that emergency crews arrived at the crash scene by both air and sea within five minutes.
New York City Mayor Bill de Blasio was briefed about the crash.
According to FlightRadar24.com, a website that tracks flight patterns, the helicopter -- tail number N350LH -- took off from Kearny, New Jersey.
It flew by the Statue of Liberty -- where someone aboard another chopper snapped photos of the chopper -- before heading toward the East River.
It flew over the Brooklyn Bridge, according to the radar path, before losing contact and crashing in the river.
The National Transportation Safety Board is sending members to investigate, and is expected to hold a news conference on Monday.
Calls to Liberty Helicopter seeking comment on the crash were not immediately returned.
ABC News' Karma Allen, Josh Margolin and Mark Crudele contributed to this report.