“We do not know the cause of this incident,” de Blasio told reporters.
But he also said there is “no ongoing threat to New York City based on all the information we have right now.”
“No indication that there was any terror nexus here,” de Blasio said.
Tenants of the building, known as the AXA Equitable Center, include BNP Paribas, Citibank and the international law firm Willkie Farr Gallagher.
BNP Paribas CEO Jean-Yves Fillion told CNBC that the 2,000 bank employees working in the building were all evacuated safely. The firm occupies multiple floors up to the 33rd floor.
Fillion said he knew something had happened when the helicopter hit the building. “We definitely felt it,” he said. He added that the company is operating normally, though he isn’t sure when employees will be allowed back into the building.
Fire trucks and police vehicles swarmed the area on the heels of the crash. While some debris from the incident fell from the roof, none of it hit anyone on the ground, authorities said.
“This building is safe,” said FDNY Commissioner Daniel Nigro.
Three sources who spoke with NBC News said that before the chopper crashed, its pilot reported having mechanical failure or engine trouble.
The aircraft had taken off from the helipad at West 34th Street on the Hudson River and planned to go in the direction of the Statue of Liberty, which is several miles south of there, according to sources.
The crash occurred a mile or so north of where the helicopter took off.
New York Police Commissioner James O’Neill said the area around the crash scene is subject to a temporary flight restriction order because of its proximity to Trump Tower, the New York residence of President Donald Trump.
That restriction means that an aircraft would need permission from the flight tower at La Guardia Airport in Queens, New York, to enter the area.
New York Gov. Andrew Cuomo spoke to reporters at the scene.
“There was a helicopter that made a forced landing or an emergency landing on the roof of the building for one reason or the other,” Cuomo said. “People in the building said they felt the building shake.”
“It was hard landing,” Cuomo said. “In the building itself, nobody has been hurt.”