The NTSB had a team of 10 investigators at the scene on Fridaty, NTSB Chair Jennifer Homendy said. The team had begun examining the wreckage, which has been moved inside a building for closer review.
"Everything is off the table," Homendy said.
"We don't rule anything out."
The tour helicopter plunged upside down into New York City's Hudson River on Thursday afternoon, killing all six people on board, including a Spanish family with three children and the pilot.
The victims included Agustin Escobar, CEO of Rail Infrastructure at Siemens Mobility, the train transportation arm of Germany-based technology company Siemens, a company spokesperson told Reuters.
Homendy said the pilot had about 788 hours of flight experience through late March. She added that dive teams were searching for components including the main rotor and tail structure that are believed to be in the river.
Video of the crash showed what appeared to be a large object plummeting 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, had departed at about 3pm from a downtown helicopter pad and flew north over the Hudson, 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 Jersey City.
Divers helped remove the victims - the pilot, another two adults and three children - 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 the website Viator. Many of the operators also offer helicopter shuttle services to the area airports.
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.
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 an Army helicopter on Jan. 29 near the Washington DC's Reagan National Airport.
The FAA has since permanently restricted helicopter traffic near the airport and is reviewing helicopter operations near other major airports.
