Agustin Escobar, an executive at Germany-based technology company Siemens, was among those killed according to the New York Times, which cited unnamed law enforcement sources.
New York City police referred requests for confirmation that Escobar was aboard the helicopter to the US Coast Guard. The Coast Guard said in a statement that it did not yet have the names of the victims. Siemens did not immediately respond to a request for comment outside normal business hours.
Video of the crash showed what appeared to be a large object plunging into the river, followed seconds later by what appeared to be a helicopter blade. Afterwards, emergency and police boats were seen circling around a patch of river where the helicopter was submerged, with only what appeared to be the aircraft's landing gear poking above the water's surface.
The Bell 206 chopper, operated by New York Helicopter Tours, departed about 3pm on Thursday from a downtown helicopter pad and flew north over the Hudson River, New York Police Commissioner Jessica Tisch said.
It turned south when it reached the George Washington Bridge and crashed minutes later, hitting the water upside down and getting submerged near Lower Manhattan about 3.15pm, just off Hoboken, New Jersey, Tisch said.
Divers helped remove the victims from the water. Four were pronounced dead at the scene, while two others were taken to area hospitals where they died.
The airspace around Manhattan is crowded with helicopters offering tourists a bird's-eye view of the sights, with at least two dozen operators listed on tour website Viator. Many of the operators also offer helicopter shuttle services to the area airports.
New York Helicopter Tours, which offers sightseeing flights for as little as $US114 ($A183) per person on its website, did not respond immediately to a request for comment about the crash.
Transportation Secretary Sean Duffy said the tour helicopter was in Special Flight Rules Area established in New York that means no air traffic control services were being provided when it crashed.
The Federal Aviation Administration and the National Transportation Safety Board will investigate, with the NTSB leading the investigation.
Duffy said the FAA was also launching a Safety Review Team on Thursday evening. NTSB Chair Jennifer Homendy and a team from the board will arrive in New York later on Thursday and plan to hold a press briefing on Friday.
New York City has a history of accidents involving helicopters. In 2018, five passengers aboard a helicopter died when it crashed into the East River, while the pilot survived. The helicopter was on a charter flight that featured an open door to allow passengers to take photographs of the skyline.
A New York City Police spokesperson said that police boats had assisted in Thursday's rescue efforts.
Helicopter safety has been a topic of discussion in the US Congress after 67 people were killed in a crash between an American Airlines regional jet and Army helicopter on January 29 near Reagan National Airport in Washington DC. The FAA has since permanently restricted helicopter traffic near that airport and is reviewing helicopter operations near other major airports.Â
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