The tour company involved in the helicopter crash that killed six people when it plunged into a New York City river last week has been shut down.

Meanwhile, what could be the most important piece of evidence yet has been retrieved from the water.

The helicopter was piloted by Sean Johnson and had a family of five on board visiting from Spain — Agustin Escobar, CEO of the Spanish branch of the technology company Siemens, Merce Camprubi Montal, the granddaughter of former FC Barcelona president Agustí Montal Costa, and their three children aged 4, 8 and 10.

All six people were killed when the Bell 206 helicopter from the tour company New York Helicopter broke apart midair and went down inverted in the Hudson River on Thursday afternoon (Friday morning, Australian time).

The US Federal Aviation Administration confirmed in a statement on Sunday (Monday AEST) that New York Helicopter Tours is “is shutting down their operations immediately”.

“The FAA will be launching an immediate review of the tour operator’s license and safety record,” the federal government agency added.

On Monday (Tuesday AEST), the main rotor was finally recovered from the river.

A video of the incident on Thursday had showed the rotor blades falling from the sky separately from the helicopter. (Watch in the video player at the top of this story).

The retrieval is significant given the helicopter was not equipped with any flight recorders.

“No onboard video recorders or camera recorders have been recovered and none of the helicopter avionics onboard recorded information that could be used for the investigation,” the National Transportation Safety Board said.

While New York Helicopter owner Michael Roth told the New York Post that he had “no clue” what happened, he said from watching video footage of the crash, he could confirm the main rotor blades weren’t on the helicopter.

Side-scanning sonar is being used to find wreckage in the Hudson River.

The doomed helicopter had its most recent major inspection on March 1, and on the day it broke apart, it was on the eighth flight of the day.

Mr Roth told The Telegraph the pilot had actually radioed base to say they were returning to the helipad before the crash.

“He called in that he was landing and that he needed fuel, and it should have taken him about three minutes to arrive, but 20 minutes later, he didn’t arrive,” Mr Roth told the publication.

He said another one of his pilots had flown over the river and seen the helicopter upside down in the water.

Four of the victims were pronounced dead on scene and two succumbed to their injuries after being taken to hospital, NYPD Commissioner Jessica Tisch said.

Joan Camprubi, the brother of Merce Camprubi Montal, said in a press conference they wanted to move the family’s bodies back to Spain as soon as possible to put them to rest.

“They left together. They left without suffering and they left with a smile on their faces and that’s important for us,” he said.

The family were last pictured smiling and posing for photos with the helicopter before takeoff.

The New York Times spoke to other families who went up in the same chopper that day before the Escobar family.

They included a father and teen son from Iceland, for which it was the father’s second helicopter flight with the company, and a French mother and father with their 7-year-old son.

The father from France, Lionel Carles, described it as a “wonderful experience” and New York tourist attraction the stood out.

The US Federal Aviation Administration will host a helicopter safety panel on April 22 to discuss risks and additional mitigation options at plane and helicopter hotspots across the country.