The 34-year-old pilot suffered just a minor hand injury after the hard splashdown on Wednesday, and was recorded by bystanders who saw the aircraft in trouble and whipped out their mobile phones.

No other people were aboard but a dock worker trying to avoid the descending aircraft slipped and injured his wrist, officials said.

The helicopter, a charter aircraft, was hauled out of the water on Wednesday afternoon by a marine crane after about 90 minutes in the river.

At a news conference, authorities said the pilot had just taken off from the helipad after refuelling when something went wrong.

"All of a sudden, he felt the helicopter go down," said Police Department Assistant Chief Stephen Hughes.

A mobile phone video of the helicopter going down, taken by a WCBS TV editor, showed it descending into the river about 45 metres from the helipad.

The aircraft came down quickly, but it wasn't in freefall. Its blades were rotating. Emergency pontoons inflated moments before it hit the water.

The pilot, who was not immediately identified by authorities, quickly scrambled on to the aircraft's pontoons.

The helicopter eventually capsized and sank mostly beneath the water but was kept from going to the bottom by the floats.

The FAA identified the helicopter as a Bell 206.

New York City has a history of both minor and major helicopter wrecks and crash landings.

Five people died when a sightseeing helicopter crashed into the East River last year. Three people died in another crash into the same river in 2011. Nine people died in a collision between a sightseeing helicopter and a small plane in 2009, not far from the scene of Wednesday's mishap.

Australian Associated Press