Police declared a "major incident" after the explosion occurred last evening on a stretch of road containing commercial and residential properties in Hinckley Road area of Leicester, over 143 km away from London with a large Gujarati-origin population.
Four people were killed in the explosion and subsequent fire that destroyed the building which consisted of a shop premises on the ground level and a two-storey flat above it, police said.
Police Superintendent Shane O'Neill warned that the toll may rise further as the emergency services are still conducting a search and rescue operation and it is unclear if more people were trapped in the rubble.
British police said there was no indication at this stage that the explosion was linked to terrorism.
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"The cause of the explosion will be the subject of a joint investigation by the police and Leicestershire Fire and Rescue Service," police said in a statement.
The emergency services said they were called to reports of a blast shortly after 7 pm (local time) and six fire engines were sent to the scene, the BBC reported.
A fire service spokeswoman said the property was a two-floor building with a loft conversion that had suffered a "pancake collapse".
The emergency services have cordoned off about 60 houses in the area, which was a mix of apartments and small shops, including a convenience store, a kebab restaurant and a Polish grocery.
"The building had gone down and people were trying to help where they could by taking the bricks off. But the fire was getting bigger and bigger so people were told to leave the scene," she told BBC.
She said she and others helped a boy, believed to be aged about 15, who was hurt in the blast.
"He was in there when it happened. I think he was in the flat above the shop. We were keeping him warm and assuring him he'd be OK and the ambulance would be there," she said.
"I've never experienced anything like this. It sounded like those big, loud boom speakers that people have in their cars, real vibration. The bass sound was so loud that it shattered the car windows," he told the BBC.
"The flames started more or less upstairs so I thought it must be something to do with upstairs, the flats. My immediate worry was when I saw the floorboards, all the wood on the floor level, I thought there must be people in the shop trapped," he said.
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