There were no immediate reports of any serious injuries.
Federal Aviation Administration spokeswoman Laura Brown said Flight 1549 had just taken off from LaGuardia Airport en route to Charlotte, N.C., when the crash occurred in the river near 48th Street in midtown Manhattan.
The plane, an Airbus 320, took off at 3:26 p.m. and went down minutes later, Brown said.
"There were eyewitness reports the plane may have flown into a flock of birds," Brown said. She added, "Right now we don't have any indication this was anything other than an accident."
Doug Church, spokesman for the National Air Traffic Controllers Union, said that the pilot reported a "double bird strike" about 30 to 45 seconds after takeoff and said he needed to return to LaGuardia.
The controller instructed the pilot to divert to an airport in Teterboro, N.J., for an emergency landing, Church said.
The plane was submerged in the icy waters up to the windows when rescuers in Coast Guard vessels and ferry boats arrived, opened the door and pulled passengers in yellow life vests from the aircraft, whose fuselage appeared intact. The plane was sinking in the near-freezing water on one of the coldest days of the year, with the mercury around 20 degrees.