There were six people on the Eurocopter AS350, which was registered to Liberty Helicopters and was being used for a private charter photo shoot.
It went down near Gracie Mansion, the mayoral residence near the northern end of Roosevelt Island, at about 7pm local time.
The sixth person – the pilot – freed himself and was rescued by a passing tugboat, according to police. He was taken to hospital but is in a good condition.
Witnesses had described seeing one person emerge from the helicopter and wave their hands for help.
Daniel Nigro, Commissioner of the New York City Fire Department, said the helicopter had been upside down and completely submerged in 50ft of extremely cold water.
The passengers had been tightly harnessed and the harnesses had to be cut to free them, he said.
The divers worked very quickly, as fast as they could.
Everyone worked very hard.
Xinran Jiang, who lives on Roosevelt Island with her husband, said they saw a red helicopter rapidly descending near the north end of the island at about 7.08pm.
She told the New York Times that the helicopter showed no obvious signs of trouble before going into the river.
It almost looked like it was landing, Ms Jiang said.
It wasn’t moving fast.
Then the next minute, it was diving into the river.
Brianna Jesme, 22, an Upper East Side resident who witnessed the crash, told Reuters TV It kind of hit sideways and just flipped over.
New York Governor Andrew Cuomo said Our thoughts and hope for safe recovery are with those who were aboard.
We are thankful for our first responders at the scene.
The helicopter has been recovered and towed to a nearby pier.
It is not the first helicopter crash in the area. In October 2011, a crash in the East River killed a British tourist and injured three others.
In 2009, a sightseeing tour collided with a small private plane over the Hudson River, killing nine people.
Another helicopter crashed into the Hudson River in July 2007 with no casualties, and two helicopters crashed into the East River during the same week in June 2005, with more than a dozen people injured.
News Source SkyNews