Updated, 2:09 p.m. | Two brothers who worked together as window-washers fell from the roof of a 45-story luxury apartment building on the Upper East Side of Manhattan around 10:15 a.m. today when the scaffold they were standing upon gave way. One brother was killed immediately, and the other was in critical condition at the Weill Cornell Medical College of NewYork-Presbyterian Hospital, according to the Fire Department.

It appeared that the scaffold had not been properly secured to side of the building, the Solow Tower at 265 East 66th Street, said Seth Andrews, a Fire Department spokesman. Almost immediately after the brothers stepped onto the scaffold from the roof of the building, it gave way, he said.

The brothers were near the roof of the building, between Second and Third Avenues, officials said. The office tower is adjacent to a brick six-story apartment building, and the brothers fell into the space between the two buildings. Parts of the scaffold and the body of the dead worker were in a plaza area between the two buildings. As it collapsed, the scaffold apparently struck a fence between the two buildings; severed sections of fence and barbed wire could be observed from the street.

At 12:15 p.m., police officers removed the body of the dead man, covered by a white sheet, on a stretcher.

No one else was injured in the accident.

Pedro Nuñez, 32, who was doing painting work on the fifth floor of a building across the street from where the accident occurred, said, “I was painting, looking out the window, and I saw the scaffolding come down very fast.” He said it fell too quickly for him to see the men on the scaffold, and added that he heard a loud crash.

Mr. Nuñez said he had occasionally talked to the brothers; he said he did not know their names but that they had told him they were from Ecuador.

According to an online database maintained by the city’s Buildings Department, the Fire Department requested an inspection of the building in February after pieces of glass dislodged from the facade of the building and fell to the sidewalk below. The owners of the building were cited for failure to maintain the exterior wall.

The men worked for Citywide Window Cleaning of Jamaica, Queens, officials said.

The Solow Tower, run by the Solow Management Company, is clad in black glass. It was built in 1979.

“This tragic accident involved outside contractors and we extend our deepest sympathies to the family of the workers involved,” Michael Gross, a spokesman for Solow Management, said in a statement. “We are gathering information and cooperating with authorities who are investigating this event.”

The company’s president, Sheldon H. Solow, is a prominent real estate investor and developer who is seeking to turn the former site of a Consolidated Edison power plant along the East River — the largest stretch of undeveloped, privately owned land in Manhattan — into a $4 billion development of seven towers, along with a public pavilion and 4.8 acres of gardens, lawns and esplanades. Some critics have expressed concern that the development, along First Avenue between 38th and 41st Streets, would loom over the United Nations headquarters complex, immediately to its north.