The chopper was said to be “flying erratically” before it crash landed on the AXA Equitable Center building on 7th Avenue, which is close to the Empire State Building and Times Square.
It had also been flying within restricted airspace, where aircraft are forbidden from flying below 3,000ft (914 metres) within a one-mile radius of Trump Tower.
The tower is just a few blocks from the site of the crash.
Authorities say the helicopter had taken off from a pad on Manhattan’s east side at 1.32pm local time, and had crashed on the skyscraper just 11 minutes later.
It is not currently clear whether the pilot had been in touch with air traffic control at La Guardia Airport, or with another tower.
‘If you’re a New Yorker, you have PTSD from 9/11’
New York Mayor Bill de Blasio said there was no indication that the crash was an “act of terrorism”, and said the person who died was believed to be the pilot.
He added: “The helicopter is pretty obliterated at this point. It was obviously a very hard hit.”
No other injuries were reported.
Witnesses described the weather as “very foggy” at the time of the crash. Pic: FDNY
New York Governor Andrew Cuomo arrived at the scene shortly after the incident, and offered reassurances to those who were reminded of the September 11 terrorist attacks.
“If you’re a New Yorker, you have a level of PTSD from 9/11,” he said.
“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.” But, he added, there were no suggestions of a terror attack.
Donald Trump, who said he had been briefed, praised the “phenomenal job” carried out by emergency services, and those still at the scene.
In a further statement, the US president described the crash as a “big tragedy” and a “very, very sad event”.
He added: “The federal people are working with the city and state people and they’ll have a full report very soon.”
The helicopter crash landed on the AXA Equitable Center building
The skyscraper was evacuated after the crash, with many of those inside describing how the building shook as the helicopter made impact.
Nathan Hutton, who works on the 29th floor, said: “It felt like you were just standing there, and someone takes their hand and just shoves you.
“You felt it through the whole building.”
Another witness who was also in the building at the time told ABC News: “You could smell the smoke coming down from the upper floor and it smelled like burning construction material.”
He added: “When we got to the first floor… that was when we were told, ‘Everybody get out now’.”
Meanwhile, an umbrella seller on the street below said he heard a “rumble”.
He said: “I didn’t see it, but I felt it. Smoke was on top of the building.”
The pilot of the helicopter is thought to have been killed in the crash
Emergency services blocked the streets with dozens of fire engines and police cars, and bystanders were warned to stay away as work continued to stop fuel leaking from the helicopter.
The weather in New York was wet and cloudy around the time of the crash, with one witness in an adjacent building describing the site as “very foggy”.
The National Transport Safety Board will investigate the crash
Sky News correspondent Hannah Thomas-Peter said: “There’s very limited visibility – it’s raining really hard.”
The privately-owned helicopter was a twin-engine, lightweight Agusta A190E. The Federal Aviation Administration said it would release details of the registration once the pilot’s name had been confirmed.
It added that the National Transport Safety Board (NTSB) would investigate the crash.
The NTSB has not yet responded to Sky News’ request for comment.
