Sandrock said the tenant was burned on 60 percent of her body and is being treated at Crozer-Chester Medical Center in Upland, Delaware County.
Rachel M. Nunn, 26, remained in critical condition Sunday afternoon, a hospital spokeswoman said.
Another resident was taken to Our Lady of Lourdes Medical Center in Camden. Police said her injuries were minor.
On Sunday afternoon, the apartment's charred remains, fenced in by a restoration crew, had become a spectacle for neighbors and passersby. People from Audubon and Mount Ephraim made the short trek over and captured the wreckage on their iPhones.
The contents of the home were strewn about the front yard for anyone to see: piles of wood, broken window frames, a purple exercise ball, a wig, clothes wrapped around tree branches, empty Gatorade and water bottles, a fire extinguisher. Two cars were parked inside the fenced area, apparently unscathed.
"Oh my God. Oh my God," neighbor Judy Liby whispered as she walked by. "Just seeing the debris..." she mused. "Ay-ay-ay-ay-ay."
Nunn's cat, a black Maine coon with green eyes, is believed to have escaped the building, and Nunn's friends are still looking for him, police said.
Camden County spokesman Dan Keashen said the Bureau of Alcohol, Tobacco, Firearms and Explosives came to the apartment Saturday night, and utility crews from PSE&G were on scene to inspect the gas lines. The Camden County District Attorney has taken over the investigation.
Gas service to the building is cut off, but neighbors are not affected, according to PSE&G spokesman Mike Jennings.
There were no reports of outages or service problems at the building before the explosion, Jennings said. The Haddon Heights Police Department issued a statement Sunday morning praising people who came to the victims' aid.
"We want to thank the immediate response of neighbors whom most likely saved the life of one of the victims: THANK YOU!"
Police declined to identify the Good Samaritans, but in an interview with 6ABC Saturday night, passerby Jessica Pastoriza described running into the building to find a woman screaming on the second floor.
"When I was inside, I couldn't see anything. I felt the heat," Pastoriza said. "I hear 'Help me, help me.' I ran out, I see a girl on the second floor, ripping her clothes off and her skin's coming off with it," said Pastoriza, 20.
Keashen said that by the time he arrived, the building was a hollow shell. "That was far and away the wildest thing I'd ever seen, from an emergency management perspective. The apartments were gone, down to the first floor," he said.
Contact Jessica Parks at 610-313-8117, email@example.com or follow on Twitter @JS-Parks.