It was not immediately known how many people were aboard the aircraft.
"A helicopter earlier this evening descended into the East River near East 90 St.", said the New York Police Department (NYPD) on Twitter. At least one person was rescued from the water, he said.
Witnesses reported the helicopter hitting the river sidewards and then inverting.
Helicopter Crashes in East River Off Manhattan, Officials Report
They Mayor's spokesman Eric Phillips said the Mayor had been briefed by the police and fire commissioners. Three other passengers remain in critical condition.
A helicopter on a sightseeing tour of Manhattan crashed into the Hudson River in July 2007, shaking up the eight people aboard but injuring no one.
The helicopter became nearly completely submerged in water. At the time, the temperature was below 40 degrees Farenheit (4 degrees Celsius).
BJP will win bypolls with big margin: Adityanath
The voting for the Lok Sabha by-election for two constituencies of Uttar Pradesh, Gorakhpur and Phulpur, began on Sunday morning. The Bahujan Samaj Party (BSP ) and the Rashtriya Lok Dal (RLD) have extended their support to the SP candidate.
Witnesses say the Eurocopter AS350, a model tourism companies tend to use, filled with water quickly after it went down.
The helicopter reportedly crashed near 89th Street in Manhattan around 7 p.m. Sunday. In the video the helicopter appears to hit the water and then tip over.
The Federal Aviation Administration and the National Transportation Safety Board are investigating the cause of the crash.
Travel warning issued for Playa del Carmen due to security threat
USA citizens are warned not to travel to five Mexican states including Colima, Guerrero, Michoacán, Sinaloa, and Tamaulipas. It was just two weeks ago an explosion rocked the ferry from Playa del Carmen, injuring 25 people, including two Americans.
This is a developing story and will be updated.
Stephen Curry heads to locker room
Midway through the second quarter, though, the team announced that Curry wouldn't be making a comeback later Thursday evening. Bryn Forbes' 3-point try from the top to tie it hit the front rim as the final buzzer sounded.