PHILADELPHIA (AP) — A four-story building being demolished collapsed Wednesday on the edge of downtown, injuring 12 people and trapping two others, the fire commissioner said.

Rescue crews were trying to extricate the two people who were trapped, city Fire Commissioner Lloyd Ayers said. The dozen people who were injured were taken to hospitals with minor injuries, he said.

The collapse involved a building that once housed a first-floor sandwich shop. It collapsed, sending debris onto a Salvation Army corner thrift store next door. The two are adjacent to an adult bookstore and theater that had been taken down earlier.

Rescuers were using buckets and their bare hands to move bricks and rubble to search for survivors.

Witnesses said they heard a loud rumbling sound immediately before the collapse.

Veronica Haynes was on the fifth floor of an apartment building across the street.

"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."

Roofers Patrick Glynn and Anthony Soli were working atop a nearby building when they heard what sounded like two loud bangs or explosions. They immediately ran down the scaffolding to look for victims, and helped pull out two women and a man.

Glynn said he had been watching workers take down the building next to the Salvation Army 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."

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.

Bernie DiTomo was driving past Salvation Army building in his white pickup truck, on his way to an appointment, when the accident happened.

"The next thing you know, I heard a rumble, and a building and a sign fell on my truck," he said.

He said he lay down in the seat of his cab. It was probably over in about 30 seconds, he said. There was a lot of dirt and dust that he breathed in, but he was able to open the door and get out, unhurt. His truck remained nearby, partially covered in debris, as DiTomo watched recovery efforts from across the street.

High school student Jordan McLaughlan said he saw several people on the ground being given oxygen by rescuers after the collapse.

"It was hard to breathe, there was a lot of dust everywhere," McLaughlan said.

The accident happened at 10:45 a.m. Wednesday on the western edge of downtown, between the city's business district and its main train station.