Witnesses have told how a man seriously injured in a suspected gas explosion at a house in Darlington, screamed that he was "on fire".
The man, who has not been named, suffered life-threatening injuries in a blaze at the semi-detached property in Wordsworth Road on Monday evening.
Durham Police said a "large explosion" had been reported in the area.
The man was taken to the Royal Victoria Infirmary in Newcastle, where he remains in a critical condition.
Neighbouring properties were evacuated as a precaution and a joint police and fire service investigation is under way.
One eyewitness told BBC Tees: "I pulled up last night from work, got out of the car and noticed the roof had exploded.
"Me and a friend up the road rushed to the scene. At that point we realised the lad was in the back garden. He was partially on fire. My friend went over to his aid.
"We went through the front windows to make sure no-one was in.
"People had seen him in the back screaming and shouting he was on fire. We did what we could at that point and told emergency services."
Another witness told how she heard a "big boom" and saw the street "light up". She said she called for the fire brigade and ambulance service after being told the man was on fire.
Ch Insp Sue Robinson said: "Three fire appliances, police and ambulance all attended the scene.
"Six people were evacuated from nearby houses.
"We are working with our colleagues at County Durham and Darlington Fire and Rescue Service to establish the cause.
"A police cordon is still in place and will remain there for the foreseeable future.
"We would like to thank local residents for their cooperation."