The only injuries reported were minor cuts to the feet of two nearby residents who stepped on broken glass after the house fell, said police Chief Inspector Joe Sullivan.
Philadelphia Gas Works employees were also at site, having shut off the gas main that supplied the building. When neighbors, 15 to 20 of whom were evacuated, were first allowed to return, they said, they were told not to smoke.
That ban was later lifted, and most residents were able to return safely to their homes after being briefly interviewed by officials.
Neighbors said they heard a large explosion.
"The boom came down, and then we saw smoke and all this glass," said Andrea Anderson, who was in the backyard of her home directly across from the collapsed home. "You felt it. I was actually in my yard and we could feel it."
Her 10-year-old daughter, Breann, was in the pool at the time. The pool water shook, she said, so she hid under the pool ladder, scared.
The house was being renovated, said Deputy Fire Chief Robert Coyne. It had been occupied for several years. Anderson said she had called police last summer about copper thieves entering the house.
There was no fire after the reported explosion, Coyne said, which he said was "very weird."
Searching and clearing the scene could take several hours, Sullivan said, so the fire, police, and Licenses and Inspections personnel on scene were taking care to stay hydrated and rest frequently. Firefighters at a nearby fire had struggled with the weather, with some complaining of heat exhaustion, so those responding to the building collapse were taking particular caution, including working in rotating shifts.
By 4 p.m., the fire trucks and other emergency vehicles blocking Torresdale Avenue had been moved, and traffic was flowing freely again.
Contact Jonathan Lai at 856-779-3220.
Pat Mazurek of the Inquirer staff contributed to this article.