The helicopter that struck a New York City skyscraper took off from a Manhattan helipad and was in the air for about 11 minutes before it crashed, authorities say.

Police Commissioner James O'Neill said that the privately owned aircraft took off from a pad on the East River.

He says it may have been headed to its home airport in Linden, New Jersey.

Fire Department officials at the scene of the helicopter wreckage on the roof on the 7th Ave building in Manhattan. Photo / FDNY
Fire Department officials at the scene of the helicopter wreckage on the roof on the 7th Ave building in Manhattan. Photo / FDNY

The helicopter struck the 228m-tall AXA Equitable building just before 1.45 pm local time.

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New York City Mayor Bill de Blasio said it isn't clear why the helicopter went down.

The mangled roof at the scene of the helicopter crash in Manhattan. Photo / FDNY
The mangled roof at the scene of the helicopter crash in Manhattan. Photo / FDNY

The helicopter was flying in rain and heavy clouds. From the river, it veered into Manhattan airspace that is supposed to be off limits for security reasons.

The pilot was killed. Officials didn't immediately release his name.

O'Neill said the aircraft was used for executive travel.

A flight restriction in effect since US President Donald Trump took office bans aircraft from flying below 914m within a 1.5km radius of Trump Tower, which is just a few blocks from the crash site.

It wasn't clear why the pilot flew into that part of Manhattan, but authorities called it an emergency landing.

Trump said in a tweet that he'd been briefed on the crash. He said first responders on the scene did a "phenomenal job."

Videos posted by onlookers showed emergency vehicles in the street, but no obvious damage to the skyscraper.

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- AP