"It is suspected that a natural gas explosion occurred, but this has to be confirmed with physical evidence," said Beloit Fire Chief Brad Liggett.
The two people injured, a 33-year-old woman and a 37-year-old man, rented the home from James and Beverley Long. They were taken to hospitals and treated for burns.
One pet died and another survived, and the residents were trapped after the explosion blew out the walls and the roof crashed down on the rubble.
A special rescue team was activated to pull the victims from the rubble as firefighters evacuated nearby homes.
"It's a tedious process because there's a lot of debris and we don't want the building to collapse any further," Liggett said.
Rescuers put in bracing so the rubble wouldn't shift, then tunneled into the debris and repeated the process.
"There was a lady in there and she was saying, 'Help me, help me, I can't move my legs,'" neighbor Diana Smith said. "We kept on telling her that help was on the way."