NEW YORK » Seven people were injured Sunday morning by falling debris after an air-conditioning unit being hoisted by crane to the roof of a 30-story midtown building broke loose, slamming into the structure and plunging to the street, officials said.

Two construction workers were taken to Bellevue Hospital Center and two pedestrians injured by falling debris were treated at NYU Langone Medical Center. Three other pedestrians were injured but refused medical attention at the scene on Madison Avenue.

Those taken to hospitals were listed in stable condition, said FDNY Assistant Chief Ronald Spadafora.

The unit fell in an area of midtown usually teeming with pedestrians and vehicle traffic during the week.

When the first 911 calls came in at about 10:45 a.m. Sunday, the area was quiet. Some residents of nearby apartment buildings said they slept through the initial crash. Others were startled by a sudden jolt.

Eileen Travers, 47, was at home with her two teenage daughters nearby when the crane collapsed. She said she heard a loud boom, went to her window and could see nothing but smoke and debris.

“You couldn’t see beyond the corner,” Travers said.

Mayor Bill de Blasio, who arrived at the scene with other city officials Sunday afternoon, said by the looks of the spread of debris on a closed section of the street, it could have been much worse.

“Thank God no one was seriously injured,” de Blasio said at a news conference near the damaged building. “There were pedestrians passing by and luckily it occurred during an hour of the day when not too many people are around.”

Officials with the city’s building department said it was not known what caused the unit to break free.

On Sunday afternoon, Madison Avenue between 36th and 41st streets remained closed as workers cleaned the area of metal, fiberglass and glass after the air conditioning unit plummeted to the street, crashing into the building as it fell.

NYPD officers were allowing only residents into the closed-off area.

The air-conditioning unit, which broke into parts to reveal jagged edges of steel, remained on Madison Avenue on Sunday as the investigation into how it broke loose continued.

Nearby, other debris was scattered across Madison Avenue. Up above, a large gaping hole was visible just below the roof of the office tower.

At about 2:30 p.m., about a dozen workers began the arduous task of removing the crane.

An hour later, the crane rested on its side on Madison Avenue as the workers prepared to load it onto a flatbed truck. By 3:45 p.m., the crane was loaded onto the truck and driven away.

The closed stretch of Madison Avenue will likely be sealed off to pedestrians and traffic for the rest of the day, but de Blasio said city officials hope to have the busy midtown thoroughfare opened by the Monday morning rush hour.

It was unclear whether the crane that was hoisting the unit had passed its most recent inspection, said Rick Chandler, the commissioner of city’s building department, but it “looks structurally sound.”

Chandler said construction work on the building started in February and “we have had no complaints.”

Alvarez is a special correspondent. Ivan Pereira contributed to this story.