Ten people have been injured, at least two seriously, after an explosion "flattened" two houses and badly damaged a third, emergency services said.
One man, believed to be in his 70s, is in a life-threatening condition after the blast in Clacton, Essex, at around 8.30am.
Neighbours could be seen clambering over the rubble to help immediately after the explosion as the remains of the roof dangled precariously overhead.
Some 19 properties have been evacuated and the walking wounded include one young teenager, Essex Police said.
Resident Stuart Coe told Sky News: "We were sitting there having breakfast and the next thing we heard this almighty bang and literally everything shook in the house - the conservatory shook, it felt like the roof was shaking.
"Obviously, the kids were upset and crying, we didn't know what was going on. And then we started fearing there had been an explosion and one of the neighbours believes she saw British Gas in the area yesterday.
"Within minutes of the explosion, we started hearing sirens coming down the road.
"It's like a bomb going off... It was a pretty nasty event."
Debris from the explosion "flew in all directions damaging windows and roofs" in Cloes Lane, Clacton, Essex Fire Service added.
Assistant divisional officer Lee Palfreyman, the incident commander, reported that "everyone has now been accounted for", but Darcy, a search and rescue dog, was checking the scene to ensure no casualties remain buried.
A spokesman for East of England Ambulance Service said the injured man in his 70s was a irlifted to Broomfield Hospital in a life-threatening condition after being anaesthetised at the scene by air ambulance paramedics.
A woman, believed to be in her 50s, was also taken to Broomfield Hospital with severe burns.
The spokesman said: " The other casualties were taken with serious and minor injuries to Colchester General Hospital. Injuries include burns and trauma injuries, such as broken legs.
"Five ambulances, several ambulance incident officers, the hazardous area response team (HART) and two air ambulances attended the scene and treated casualties on scene before they were taken to hospital."
A primary school in Cloes Lane, St Clare's Roman Catholic, is believed to have been evacuated.
An Essex County Council spokeswoman said: "We are awaiting confirmation but we believe the school has been cleared."
Cloes Lane resident Gwen Mitchell, 70, who lives about 30 yards from the blast scene, said the house caught in the explosion was a semi-detached property.
Mrs Mitchell, a Conservative councillor on Tendring District Council, said: "I didn't know anything about it until I had got home.
"It's about 12 to 14 houses up the road from me on the opposite side to me. There was a very strong acidy, smoky smell in the air.
"There are lots and lots of police, ambulance and fire engines in the road, and it looks like one of the houses has gone.
"My heart has been doing flips ever since I heard the news. You don't expect this to happen so close to your own home.
"I thank God that it's not me involved and I dearly hope that no one is badly injured. There is insulation being blown up the road, which I presume has come from the house, and we have had people from the gas and electricity boards here."