Firefighters believe a domestic gas fault is likely to have caused an explosion which destroyed two houses and injured 10 people.
One semi-detached house was razed to the ground and the second floor of a neighbouring property was left hanging precariously following the blast in Clacton, Essex. A third property was also wrecked.
One man, believed to be in his 70s, is in a life-threatening condition after the blast in Cloes Lane, at around 8.30am.
A woman, thought to be in her 50s, was taken to Broomfield Hospital, Chelmsford, with severe burns.
Residents said they felt tremors and were thrown from their beds by the impact. Neighbours could be seen clambering over the rubble to help immediately after the explosion.
Speaking at the scene, Paul Hill, assistant chief fire officer for Essex, said: "As far as we understand at the moment it involves domestic gas and all of our experience tells us that's probably the cause.
"If we get through this event with no fatalities we'll be overjoyed. This was an extremely powerful explosion and the adjoining properties have been left derelict."
Some 19 properties were evacuated and the walking wounded included one young teenager, Essex Police said.
Teresa Reed, who lives in nearby Towse Close, was walking to her job as a lollipop lady when the explosion happened.
"I walked past a minute before the explosion," she added.
"I heard an enormous blast and turned around to see a very confusing scene. A moment later and I could have been killed.
"I know somebody who lives nearby so I'm just praying they're okay."
East of England Ambulance Service confirmed critical care had been given to two people at Broomfield Hospital with eight others taken to Colchester General Hospital. Injuries included burns and broken limbs.
Colchester Hospital confirmed four of the casualties had been released.
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.
"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, Essex Fire Service said.
Assistant divisional officer Lee Palfreyman, the incident commander, said everyone had been accounted for, but a search and rescue dog, was checking the scene to ensure no casualties were still buried.
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: "There was a very strong acidy, smoky smell in the air.
"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."