Officials say the commercial building was in the process of being demolished when it collapsed. Authorities say the four-story building at the corner of 22nd and Market streets in Philadelphia's Center City collapsed at about 10:45 a.m. ET, damaging nearby structures.
Authorities say demolition crews were taking the building down, but one of the walls apparently fell the wrong way. The building collapsed onto a two-story building that was home to a Salvation Army Thrift Store that was damaged but is still standing.
Rescuers pulled one woman from the rubble two hours after the collapse after hearing her voice. The search for survivors will continue into the night. Thirteen people were taken to area hospitals with minor injuries, said city Fire Commissioner Lloyd Ayers.
Late Wednesday night, a 14th survivor was pulled from the rubble of the building.
Hours after the deadly accident body bags were removed from the rubble. Video footage taken at the scene showed authorities loading the body bags into ambulances.
At a Wednesday night news conference, Mayor Michael Nutter announced a total of six individuals were killed: five women and one man. They were not immediately identified.
Officials said they would keep excavating to make sure there were no other victims.
Veronica Haynes was on the fifth floor of an apartment building across the street when the collapse happened.
"I was standing there looking out my window, watching the men at work on the building, and the next thing I know I heard something go 'kaboom,'" she said. "Then you saw the whole side of the wall fall down ... onto the other building."
ABC News and The Associated Press contributed to this report.