A witness helped a family escape following the blast, which shook homes like an “earthquake” and was heard three miles away, at about 7.30am on Saturday.
Dramatic pictures posted online show a huge wall of flames moments after the explosion in Illingworth, near Halifax, in West Yorkshire, and smouldering piles of debris after the property was “flattened”.
“There is literally nothing left of the house,” one resident wrote on Facebook, while another man said the property “had disappeared”.
The blast was so powerful it shook the ground about a mile away, another local said.
The home was occupied by a couple and their teenage son, and everyone has been accounted for in the aftermath.
Engineers from Northern Gas Networks were at the scene along with firefighters and police after paramedics took the victims to hospital.
The victims were initially treated at the scene as firefighters battled the blaze. A 98-year-old neighbour was among the evacuees, said locals.
A nearby resident tweeted moments after the blast: “I am only half awake but either something just exploded near by or we had an earthquake.”
A woman said she heard the explosion three miles away in Denholme.
Another, who was about a mile away at the time, wrote on Facebook: “The explosion shook the path under my feet at Ogden.”
A local tweeted: “Felt the explosion! Thought something had hit the house and only noticed the flames on the way back upstairs from checking everything. Fire looks to be out now.”
The house was “flattened”, said a woman whose father lives across the road.
She tweeted: “It’s mad how everyone is fine. How do you anticipate an explosion like that and get out in time???”
Six surrounding houses were evacuated as a precaution, and firefighters continued to douse “pockets of fire” that were still burning some time after the explosion turned the house to rubble.