US regulators on Monday issued an emergency order grounding the helicopter tour company behind last week's deadly crash in New York.

The Federal Aviation Administration (FAA) took the action after it learned the company's operations chief -- who had agreed Sunday to halt flights voluntarily -- was fired, acting administrator Chris Rocheleau said in a statement.

A Spanish business executive, his wife and three children died along with the pilot when the helicopter operated by New York Helicopter Tours malfunctioned and plunged into the Hudson River on Thursday.

The family was on a tourism flight over Manhattan, described by the operator as the "ultimate sightseeing tour of New York City."

According to the FAA's order, the head of operations at New York Helicopter was fired shortly after he agreed to a request by the agency on Sunday to shut down flights the crash was investigated.

New York Helicopter chief executive Michael Roth notified the FAA in an email that he did not authorize a cease of operations and that the person who agreed to do so was no longer with the company, according to the FAA.

"The immediate firing of the director of operations raises serious safety concerns," the FAA said in its emergency order.

If New York Helicopter does not surrender its air-carrier certificate immediately, it will be hit with legal action including civil fines of as much as $17,062 a day until it complies, the FAA told Roth in the letter.

The civil aviation authority already announced reviews of the helicopter tour operator's license and safety record.

The National Transportation Safety Board is investigating the cause of the crash.

Jersey City officials said working theories included a drone collision, a bird strike or mechanical failure.

Video of the incident has emerged showing the fuselage apparently becoming detached from the rotor.

The crash has shone a another light on US aviation safety after a string of deadly crashes, including the collision between a military helicopter and a passenger jet in Washington in January that claimed 67 lives.

A light aircraft also crashed after departing Boca Raton airport in Florida on Friday, with local media reporting three people had been killed after the plane developed a mechanical issue.

AFP

US grounds helicopter company behind fatal New York tour