A tourist helicopter plummeted upside down into New York City's Hudson River on Thursday, killing all six people on board, including a Spanish family with three children and the pilot, Mayor Eric Adams said.

Agustin Escobar, CEO of Rail Infrastructure at Siemens Mobility, the train transportation arm of Germany-based technology company Siemens was among those killed, a company spokesperson told Reuters.

"We are deeply saddened by the tragic helicopter crash in which Agustin Escobar and his family lost their lives," the spokesperson said in an emailed statement.

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 at about 3pm ET (1900 GMT) 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 sinking near Lower Manhattan about 3:15pm, just off Hoboken, New Jersey, Tisch added.

Dani Horbiak, a 29-year-old resident of Jersey City, New Jersey, said she witnessed the crash from her window while working from home.

"I looked out my window right here, and I saw the helicopter falling to pieces, and I watched multiple pieces splashed down into the river below, and I was wondering what happened," she told Reuters. "But I'm putting the pieces together… it does sound like I was maybe hearing the propeller smacking into something."

Horbiak said she was "shaken" by the incident and later called emergency services, which said it had already dispatched responders to the scene.

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.

Bird's eye view

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's airports.

New York Helicopter Tours, which offers sightseeing flights for as little as $114 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 a Special Flight Rules Area established in New York, which 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 on Thursday and plan to hold a media briefing on Friday.

In 2018, five passengers aboard a helicopter died in New York when the aircraft 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 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 the crash of 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.