The pilot of a helicopter died after it crash-landed on top of a skyscraper in Manhattan, fire officials say.
The incident sparked a rooftop fire, which was quickly extinguished. Some workers were evacuated from the tower, but none were hurt.
The office building close to Times Square shook from the impact, New York Governor Andrew Cuomo said.
New Yorkers, he added, have “a level of PTSD from 9/11” when they hear news of an aircraft crash in Manhattan.
The pilot has been named by local media as Tim McCormack.
He was the only person aboard the twin-engine Agusta A109E helicopter, said the Federal Aviation Administration (FAA).
He added: “If you’re a New Yorker, you have a level of PTSD, right, from 9/11. And I remember that morning all too well.
“So as soon as you hear an aircraft hit a building, I think my mind goes where every New Yorker’s mind goes.”
Speaking at the White House on Monday, US President Donald Trump said the crash was “a big tragedy” and “a very sad event”.
No debris was visible on the pavement or road below the scene of the AXA Equitable building, which is about 750ft (229m) and more than 50 storeys high.
Michaela Dudley, of Hoboken, New Jersey, was working in the building that the helicopter crashed into and described feeling “a small tremor”.
“I started hearing the blare of sirens and knew something bad had happened,” the 30-year-old lawyer said.
“There was a flood of sirens outside and an announcement for us to leave the building. I grabbed my backpack and cell phone.
“The stairwell was packed with people trying to get out and so it was a really slow process. We didn’t know what was happening so people were getting a bit panicky.”
Nicolas Estevez told Reuters news agency he had been standing across the street when a 12in (30cm) chunk of metal that may have come off the helicopter landed on the pavement just feet away.
The aircraft took off from a heliport at Manhattan’s east side at 13:32 and crashed 11 minutes later, officials said.
Mr de Blasio said it was “an unusual situation for sure”, and the helicopter would have needed special permits from LaGuardia Airport in Queens, New York City.
The building is about half a mile from Trump Tower, and airspace has been under a flight restriction since he became president.
The mayor described the helicopter as “obliterated”.
“There is no indication at this time that this was an act of terror and there is no ongoing threat to New York City,” he added.
The National Transportation Safety Board is investigating the incident.
Last month a helicopter crashed into the Hudson River, falling just short of a heliport.
Five people were killed in 2018 when a sightseeing helicopter plunged into the East River.