Officials say there was a leak in a gas line going to a stove on the second floor of the three story home.
Apparently, one of the residents inside turned on the stove, igniting the blaze.
The explosion and fire injured two people and brought down the Haddon Heights home.
Crews were called aroud 3:30 p.m. Saturday to the house on the 100 block of the White Horse Pike for a fire.
Firefighters arrived to find heavy flames shooting from the home.
A second alarm was called.
"Very intense fire, you feel the heat across the street," witness Ken Whalen said.
Witnesses, including 6abc viewers, reported hearing an explosion prior to the fire.
"There were a ton of flames coming out of the roof, debris shot everywhere," witness Jeff Taylor said.
Jessica Pastoriza of Runnemede, New Jersey tells Action News she drove by the scene at the very moment of the explosion, pulled over, and ran in to rescue a woman trapped inside.
"When I was inside, I couldn't see anything. I felt the heat," Pastoriza said.
The 20-year-old says she ran into the home asking 'is anyone there?'
"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," Pastoriza said.
Pastoriza says she then helped the young woman out of the building.
Officials say the woman was one of two victims transported to local hospitals.
Pat Hovern, a coworker of the woman, showed up to the scene Saturday night.
She identified the young woman as Raquel Nunn and says she lived with her cat in the home.
Nunn is listed in critical condition at Crozer-Chester Medical Center.
The second victim was taken to Our Lady of Lourdes Medical Center as a precaution.
The two victims were the only ones in the house at the time of the explosion.
Authorities say the old Victorian house was converted into five apartment units and the blaze caused the building to collapse.
"Within minutes, the second and third floors collapsed into the first floor," Haddon Heights Mayor Ed Forte said.
Emergency services and investigators stayed on the scene until late Saturday night and returned Sunday morning.
They set up a fence around the debris.
Just before noon Sunday, the cause of the fire was determined.