According to AP, the Fire Department of the City of New York (FDNY) has also said the helicopter's pilot was killed in the crash.
It was raining heavily at the time of the crash.
New York Governor Andrew Cuomo said there was no indication of terrorism and the helicopter seemed to have made an emergency landing.
He said the 54-storey office building on Seventh Avenue shook from the impact and the crash sparked a rooftop fire.
The building the helicopter crashed in to, and many others nearby, were evacuated.
Chillingly, another added: "If you're a New Yorker you have a level of PTSD from 9/11". "We don't know what caused the helicopter to land on top of the building".
"I didn't see it, but I felt it", said Douglas. "The Trump Administration stands ready should you need anything at all", he tweeted.
The fire alarms activated and security told the occupants to get out of the building via the stairs, Hutton said.
Cuomo explained that a fire began when the aircraft hit, but is under control.
"We ran down. I think we were the first floor to evacuate, actually, because we felt it so quickly", Farrell told ABC News.
Helicopters are a regular sight in the air around Manhattan, and they have occasionally been involved in crashes. The pilot escaped mostly unscathed.
In 2006, New York Yankees pitcher Corey Lidle's single-engine plane slammed into the 20th floor of a building on Manhattan's Upper East Side, killing Lidle and his flight instructor.
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