The scene after the building collapse in PhiladelphiaDino Hazell/Associated Press

An unexpected building collapse in Center City, Philadelphia killed six and injured more than a dozen people on Wednesday, June 5.

Rescue teams were still searching the rubble for people who may have been trapped beneath the collapse.

The collapse at Market and 22nd Streets in Philadelphia occurred at about 10:40 am on Wednesday morning. A four-story building that was being prepared for demolition collapsed onto an adjacent two-story Salvation Army Thrift Store.

Patrick Glynn and Anthony Soli, who were working on a nearby building and suspected that the building might collapse, immediately ran down their scaffolding and helped pull out two women and a man after the building fell.

Glynn told CBS News he had been watching workers take down the doomed building over the past few weeks, and said he suspected a collapse was inevitable because of the methods the workers were using to tear it down.

"For weeks they've been standing on the edge, knocking bricks off," he said. "You could just see it was ready to go at any time. I knew it was going to happen."

Similarly, Steve Cramer, who has been working as a window washer across the street for several days, said the demolition crew left 30 feet of a dividing wall up with no braces and it compromised the integrity of the building

"We've been calling it for the past week — it's going to fall, it's going to fall," his co-worker Dan Gillis said.

Carlton Williams of the city's Department of Licenses and Inspections said there were no existing violations on the building and the demolition company had proper permits for the work they were doing.

An architect working for the owner of the now demolished building said they were dismantling it to make room for an apartment house.

"This is a delicate and dangerous operation," Mayor Michael Nutter said of the rescue and recovery effort during a press conference from the scene.