Ten people suffered minor injuries, including five civilians -- three who refused medical attention -- two New York Police Department personnel, two construction workers and one firefighter.
As a result of the accident, motor vehicle traffic was banned on Madison Avenue from 34th Street to 42nd Street. Cross street traffic can get through. Pedestrian traffic is banned from 37th Street to 40th Street.
Authorities say that as the air conditioning unit was being loaded onto the 28th floor, the floor buckled. Officials say, "workers experienced a sudden shaking and the floor buckling." There was a weight shift and the air conditioning unit fell. Investigators are looking at what caused the floor to buckle, saying that either the payload was too heavy for the floor or there could be a defect in the floor.
No criminality is believed to be involved in the incident.
Crews are in the process of repairing the street and removing debris from the scene. Office chairs from inside the high rise ended up on the sidewalk, and cars along the street were hit with chunks of debris.
Gregory Welch and his wife, Priscilla, were driving their black Mazda on the street below when the incident happened. Now, they're trying not to think about how close they came to death.
"I don't think about what could've been, at least I try not to," Gregory Welch said. "The airbags deployed, and the car started smoking in the front, so I said, 'We have to get out of here.'"
The car and everyone below was peppered with pieces of rubble.
"It just got foggy that quick, and boom, we heard an impact on the top and in the back," Gregory Welch said. "My daughter was sitting back there 30 seconds before."
In the cloud of dust, the couple had only seconds to get out of their car, convinced that if they stayed inside, they would die.
"We've had some close calls, but not like that," Gregory Welch said. "Plus, we thank God he was shielding over us."
Other witnesses described a terrifying scene.
"We heard an initial crash, and then some rapid-like firecrackers going off, a pack of firecrackers," witness David Katz said.
The initial crash, officials say, was the sound of the huge air conditioning unit slamming into one part of the building.
"They're trying to put this piece of mechanical equipment into the the mechanical equipment floor, which is on the top floor of the building," FDNY Chief Ron Spadafora said.
The load dropped, hit the facade and then tumbled down the tiered section. Each time it collided, it brought down parts of the building.
"There are a lot of setbacks in front of that building, and we're lucky this piece of equipment didn't fall directly into one of these set back roofs and go through the building," Spadafora said.
However, the facade was clearly heavily damaged in several spots.
The fire department and buildings department were examining surrounding buildings to determine if any are structurally compromised.
Mayor Bill de Blasio, speaking to reporters on Madison Avenue a block from the accident, called it "obviously, a very serious incident."
"Thank God, this incident occurred at an hour of the day on a weekend when there were not too many people around," de Blasio said.
The Associated Press contributed to this report.