Philadelphia Mayor Michael Nutter and Fire Commissioner Lloyd Ayers said on Wednesday afternoon that 14 people were removed from the scene.
Of the 13 injured, most were reported to have minor injuries.
There was no immediate word on the identity of the person killed.
Authorities on the scene say this was still an active search and rescue situation.
Dan Gillis said he saw the collapse happen, saying "I was working across the street doing windows. They've been working over there for about a week now. It was a 30 foot wall, they started pulling on a piece of steel, and I seen the whole wall just waving back and forth, and as soon as they pulled that out, there was no stopping it."
The collapse brought down part of the thrift store and what looks like converted row homes attached to the back of the building.
Bystanders immediately jumped into action, helping assist the wounded before first responders arrived.
Emergency crews worked feverishly to find victims trapped in the rubble.
"Our firefighters are actively engaged in a search and rescue operation. It is delicate, this is dangerous work," explained Mayor Michael Nutter. "We're going to continue this operation until we are certain that anyone who was in the building has been taken out of the building and is recovered."
Mayor Michael Nutter is asking the public to please avoid the area from 20th Street to the Schuylkill River and Chestnut Street to the Ben Franklin Parkway.
According to officials, there was an active demolition on the 4-story building at 2140 Market by a Philadelphia-based company known as Griffin Campbell Construction. There were no existing violations on the property and the contractor conducting the demolition had a license.
Stay with Action News and 6abc.com as more information becomes available.