Emergency services were called to the terraced house in Rosehill Street, near Sandford Lido, on Thursday evening.
An elderly woman rescued from the wreckage is said to be “doing well” in hospital with injuries not thought to be life-threatening.
The house was totally destroyed in the explosion.
Jon Hall, from Gloucestershire Fire and Rescue Service, said that when crews arrived they could hear the woman calling for help.
“[Crews] went in despite the risk of further collapse and worked with paramedics to get her out,” he said.
“She’s doing well, she was in remarkably good voice and she was talking to crews when they brought her out.”
Gloucestershire Police said about 20 homes on the road were evacuated.
A spokesperson said a neighbouring property would probably have to be demolished.
People living in about seven properties, who were not able to return home overnight, spent the night in the nearby Langton Hotel.
Part of Rosehill Street remains closed to traffic, the police said.
Beth Fowler, who lives close to the scene, described how she had heard a loud bang.
“My mum went out into the kitchen at first I thought she had dropped something,” she said.
“The French doors at the back of the house were blown in and all the glass smashed and our dining room ceiling is badly cracked.
“The bricks and tiles from the house that blew up have gone everywhere – it’s a complete mess.”
Rob Perry, who lives about half a mile away from the house, said he was walking up the stairs when all the windows in his house rattled.
“It was quite a powerful blast even from this distance at I first thought our house could be falling down,” he said.
The police spokesman said gas and electricity supplies were turned off in the street as a precaution.