A young child has been killed and four adults have been injured, two of them seriously, after a suspected gas explosion in Heysham, Lancashire Police said.
The explosion caused two houses to collapse and damaged several others, one significantly.
Debris from the blast covered nearby streets and fields, as residents described the noise "like a bomb going off".
Assistant Chief Constable Jo Edwards told reporters at the scene: "Tragically a young child has been killed and four persons also injured. Our thoughts are with all those affected."
Two adults are "seriously injured", she added, while "the other two remain under medical assessment".
Emergency services are still in the search and rescue phase, she added, working to "make the area safe".
Officers were called to reports of an explosion at 2.40am, she said.
The child, whose age has not been given, was declared dead at hospital said Matt House, consultant paramedic with North West Ambulance Service (NWAS).
Six ambulances, four doctors and a hazardous area response team attended the incident, Mr House said.
Ben Norman, assistant chief fire officer for Lancashire Fire and Rescue Service (LFRS), said they "think everyone is accounted for".
At its peak, he said, 80 fire officers were on the scene, including two engines from Cumbria.
Mr Norman said people should expect disruption, but he was confident there was no further risk.
Earlier, the service said on Twitter that 10 units were called to a row of homes around 2.30am and that firefighters were searching the scene.
"A major incident has been declared after we (were) called to terraced houses on Mallowdale Avenue. It has been reported that there has been an explosion at a property and firefighters are searching the collapsed property," they said.
Lancashire Police tweeted that they had put up a safety cordon and evacuated residents from nearby properties in the town some 25 miles northeast of Blackpool.
"We are asking people to please avoid the entire area while we deal with this ongoing incident," the force added.
Electricity North West said it had paused power supplies to the area for safety reasons while the blast was being investigated.
Twitter user @murphy30220538 posted a picture of the scene, saying three houses had collapsed after a "terrible explosion" that "sounds disastrous".
People also commented on the loudness of the explosion, including @jstewart668, who said people "heard the bang as far as Lancaster", around nine miles (14km) away.
@ScottLancaster6 said he "heard it in Bowerham", seven miles (11km) from Heysham.
A Gofundme page set up to help Mallowdale Avenue residents had raised more than £20,000 in just over four hours.
Heather Brandwood, manager of two pubs in nearby Morecambe, set up the fundraiser and said it was "humbling" to see the community pull together in such a way.
She said people were donating clothing and toiletries to evacuated residents.
"We are very conscious that people were evacuated from their homes with immediate effect. We have heard from an elderly couple who left in their pyjamas. There is a woman who is in literally nothing but her nightie," she said.
Electricity North West wrote on social media that it had paused electricity supplies to the area for safety reasons while the blast was being investigated.
‘I was awoken by a loud bang’: Witnesses describe scene of explosion
By Sky reporter Sadiya Chowdhury, who is at the scene
The road is littered with roof tiles. It looks like there’s been a hurricane, but the residents of Bowland Street in Lancaster are walking around the aftermath of a gas explosion.
"I was awoken by a loud bang. It sounded like a bomb went off," one resident says to me.
"It sounded like a bomb went off." He guides me through his property to the back garden which is full of debris from the blast. Roof tiles, insulation and chips of wood. "It rained down vertically on us."
Fire and rescue services are still searching the properties at the centre of the blast on Mallowdale Avenue, and a police cordon is in place.
One woman grips the hand of her child. They’re both in bathrobes.
"We’re not so far from the nuclear power station, so we were just assuming," she says. "I could see blue flashing lights, I could hear people screaming.
"Police were telling us turn off your cars and everything like that, and we had to turn off the gas.
"My next door neighbour, she’s really elderly and she was scared to go in. She’d rung three people to get away from the area but no one was answering so she was just going to walk the streets with her dog."
A major incident has been declared after the blast on Mallowdale Avenue, where just the chimney stacks of a row of terraced houses remains.