Two people have been killed when a small aircraft crashed into a building in New York City's affluent Upper East Side, police say.
Flames and smoke are coming out of the 50-storey apartment building on Manhattan island.
The FBI says there is no indication that the crash is terrorism-related. A White House spokesman said they were not ruling out any theory.
As a precaution, fighter planes are now flying over a number of US cities.
The New York Fire Department said the aircraft struck the 20th floor of a building on East 72nd Street and York Avenue - identified as the Belaire, a prestigious 50-storey residential tower.
Witnesses told the Associated Press (AP) news agency the crash caused a loud noise, and burning and falling debris was seen.
Emergency workers have rushed to the scene, while firefighters shot streams of water at the flames from the lower floors.
A freelance journalist at the scene, David Cox, added there were "hundreds" of emergency workers on the ground.
"It's just next door to a hospital so there's a large amount of people wearing doctor's coats and various other nurses gear standing round the street," he said.
Another eyewitness told the BBC: ''The plane levelled out and then the next thing I knew it disappeared behind the building and was gone.
"I said I can't believe that this is what I just saw and they kept saying it was a helicopter but it was a plane.''
A woman who lives nearby, Chris Foege, said: "I just stood there in shock, I thought 'this can't be happening to us again'. It was like 9/11 all over again," she told the AFP news agency.
BBC correspondent Guto Harri in Manhattan says there are scenes of chaos on the streets, with fire engines, police cars and ambulances blocking nearby roads.
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Oh my gosh I didn't even put those dates together! That's so odd!!! All I can say is that it's either deliberate or we'd best get our act together before issuing licenses to these pilots. I mean it wasn't a corner of a building it was right smack dab in the middle so how on earth could he/she have not seen it is beyond me.
BBC correspondent Guto Harri in Manhattan says there are scenes of chaos on the streets, with fire engines, police cars and ambulances blocking nearby roads.
I live in NY and there is no chaos. About a few blocks away, life is looking normal. It seems this was an accident, distress calls were heard by the FAA.
Seems it was a Yankee pitcher. From what I understand, flying around Manhatten is fairly dangerous for experienced pilots, and he didn't have much experience with flying.
Guys, stop with the 10/11 conspiracy theories. There was no indication of terrorism. The NY Yankee pitcher who died said a couple of days after the Yankees elimination from the playoffs that he was going to get his pilot's lisence soon. Apparently he was on with an instructor, and they were learning to curve around the statue of liberty. Distress calls were heard, but it was too late.
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