Frantic employees squeezed into the stairwell, hurrying down flight after flight, not knowing that a helicopter had just crashed on top of their building, sparking a fire and leaving one person dead.
The Federal Aviation Administration said in a statement that the aircraft was an Agusta A109E, a twin-engine, lightweight helicopter.
Andrew Cuomo said it's unclear what caused the helicopter to make the forced landing.
The crash sparked a fire that has been extinguished, though emergency workers are responding to "some amount of fuel leak", according to FDNY commissioner Daniel Nigro.
Hours after the incident, the New York City Fire Department tweeted images of the scene, showing broken and burned helicopter parts scattered atop the building.
The pilot is the handiest presumed victim, Mayor Bill De Blasio educated reporters at a day news conference.
The pilot, identified as Tim McCormack, died in the crash, law enforcement said.More news: Le Maire: Renault stake reduction a long-term goal
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"If you're a New Yorker you have a level of PTSD from 9/11.so as soon as you hear an aircraft hit a building, I think my mind goes where every New Yorker's mind goes".
The helicopter was privately-owned by American Continental Properties, which confirmed that the deceased had flown for them for the past five years. A flight restriction in effect since President Donald Trump took office bans aircraft from flying below 3,000 feet (914 meters) within a 1-mile (1.6-kilometre) radius of Trump Tower, which is less than a half-mile (0.8 kilometres) from the crash site. "It was obviously a very hard hit", de Blasio said, adding nothing indicated "an act of terrorism".
"I started hearing the blare of sirens and knew something bad had happened", the 30-year-old lawyer said.
Cuomo said the crash likely stirred memories of Sept 11 for many city residents. "It sounded like a small engine plane at first then I just felt the building shake", he said. He was chief of the East Clinton Volunteer Fire Department. The helicopter was in the air for 11 minutes prior to the crash.
"It was pretty much like an explosion going off in your cockpit, a little bit of a pandemonium kind of thing, you know, you have to gather yourself and we headed over to 30th street, McCormack told ABC 7 NY at the time".
The building at that location was purchased by the California Public Employees' Retirement System for $1.9 billion in January 2016 with partner CommonWealth Partners of Los Angeles.
ABC television reported that the pilot was a certified instructor with substantial flying experience.