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).
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She pointedly did not congratulate Ford, and continued to dispute the result. "On June 7th, we can vote to say no to it". The leadership race itself stirred strife and forced party brass to defend their decisions on a number of fronts.
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.
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This is a developing story and will be updated.
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Rios, whose organization is working with the family, said Morales-Luna's daughters are in the custody of an uncle. One of the officers hands her daughters the keys to their home before driving away with their mother.