The parapet of a vacant building under demolition as part of the Atlantic Yards project collapsed onto the street in the Prospect Heights section of Brooklyn Thursday morning.

The collapse prompted the temporary evacuation of a shelter next door, sending about 80 residents onto the street.

"All a sudden I heard a boom and then all a sudden the building started shaking," said one resident of the shelter.

Officials say the parapet on the former Ward Bread Bakery Complex came crashing onto the sidewalk and Pacific Street just after 9:45 a.m. No workers were reported injured, and no pedestrians were struck.

Pieces of the parapet littered the sidewalk and crashed onto some cars.

The parapet is the barrier at the edge of a structure employed to prevent persons or vehicles from falling over the edge.

Concerns about the building leaning prompted officials to evacuate the shelter on the block out of an abundance of caution. The Buildings Department was sending inspectors to look at the building.

Officials say the building owner has retained a contractor, Gateway Demolition, to remove debris, install a sidewalk shed and remove the remaining portion of the parapet walls on 800 Pacific Street to a safe level.

Buildings Department engineers will remain on scene as the building owner's contractor conducts shoring and remedial work at the site.

The Red Cross is assisting with the relocation of the residents to the Atlantic Terminal Senior Center.

The five-story bread bakery was being demolished as part of the Atlantic Yards project. Protestors rallied in front of the building on the first day of demolition last month.

The protesters said the historic building, built in 1911 and covered in white terra cotta tiles, is example of a "scorched earth" policy that will blight the corridor along the Long Island Rail Road yards in Prospect Heights.

The work at the bakery at 800 Pacific Street will include two months of abatement, including the removal of asbestos, Forest City Ratner Companies said in a statement. When the building is gone in two months, 75 percent of the materials will be recycled, the company said.

The Atlantic Yards project proposes a sweeping, 24-acre development with a 19,000-seat basketball arena for his New Jersey Nets, residential buildings and four soaring office towers.

The Frank Gehry-designed project would be built over Long Island Rail Road storage yards and is dependent upon the state condemning more than two square blocks of private property and knocking down up to 70 buildings.