Six people have died from the collapse of two buildings in Center City Philadelphia.
A search for additional victims continues, said Mayor Michael Nutter.
The 10:45 a.m. Wednesday collapse involved a four-story building that once housed a first-floor sandwich shop and apartments above. It was being demolished when much of the debris from the building fell onto a neighboring Salvation Army thrift store that was filled with shoppers and employees, fire officials said.
Ari Barkin was at work in a highrise office across the street when he heard and felt a loud rumbling.
"You know, typically, if a truck goes by or they're doing roofing work in any of the nearby buildings, they're very short period sounds," Barkin said. "This one continued for much longer period of time and then, of course, when I took a look, it was a plume of smoke."
Dozens of paramedics and fire crews remain on the scene as they search for any additional victims.
"Our firefighters are actively engaged in a search and rescue operation. It is delicate. This is dangerous work," Nutter said. "We have a significant number of personnel on the scene trying to see whether or not there are any other individuals possibly in this building."
A number of people were taken out on stretchers; others managed to get out of the rubble on their own, Ayers said. Six people were killed; 13 people were transported to area hospitals with minor to moderate injuries, said officials.
The collapse happened on the western edge of center city, between the city's business district and 30th Street Station.
"I was on the corner of 22nd and Market, and they were knocking down a building," said Jordan McLaughlin. "What happened was the building collapsed the wrong way and it landed on a thrift shop, and there were people inside of the thrift shop. Before the building collapsed, you saw one person walk in so, it was scary."
One woman who was on the 5th floor of an apartment building across the street said she was looking out her window, watching the work on the building, and "heard something go kaboom." Veronica Haynes said she saw "the whole side of the wall fall down" onto a neighboring building.
Two men who'd been working on a roof of a nearby building heard what sounded like two loud bangs or explosions. They immediately ran down the scaffolding and helped pull out two women and a man.