It was just another Wednesday morning for Aaron Marshall, a manager at ING Direct Cafe, at 17th and Walnut streets, until he heard a noise like an explosion about 6:45 a.m.

"I saw a dust cloud going by," said Marshall, 33, adding that cafe employees called 9-1-1. "And I went outside and there were bricks in the street."

The sound that Marshall heard was panels from the facade of the Broadcast Building, formerly the home of the Brasserie Perrier restaurant, crashing to the ground.

"We brought in contractors and engineers to investigate the facade," said Gary Silvi, of Vesper Property Group, which owns and manages the building. "We're cooperating with city officials."

Silvi said he was thankful that the facade collapse occurred before anyone was on the street, so nobody was injured. He said cleanup crews were standing by for word from city officials to begin removing the debris.

Calls to the Department of Licenses and Inspections and the mayor's press office yielded no new information yesterday afternoon.

Around noon, Walnut Street remained closed between 15th and 17th streets. Police lines extending half a block kept pedestrians from entering the scene, and pieces of debris littered the street and sidewalks.

"It looks like the architecture failed," said Dan Toor, 27, who was walking his dog, Izzy, from Spring Garden Street to Rittenhouse Square. "I can't judge, but it looks pretty dangerous."

Toor was one of dozens of onlookers who gathered to watch the crews on site.

"It's spooky," said Bob Frantz, 41, a manager of the FedEx store around the corner from the scene, as he photographed the damage with his camera phone. "That could have happened at 12:30 instead of in the morning."

Carla Bennett, 47, who works for the Philadelphia Housing Authority, walked across the blocked streets and debris about 12:30 p.m.

"I thought maybe they were trying to deliver something," she said of the crane blocking the street, adding that she was on her way to 17th Street. "That looks bad. It's kind of an inconvenience, but they have to be safe. . . . You can always go over to the next block and walk down."

Entrances to businesses on the block, including the Alma de Cuba restaurant, Urban Outfitters and Jennifer Convertibles furniture store, were blocked off as well, and police directed people who work in buildings there to use the rear entrances.

Bennett, Frantz and Toor agreed that it was a stroke of luck that no one was injured during the incident. "I don't really look up when I walk," Frantz said.

"But now I'll be looking up."