At least one person has died and three others were taken to hospital after a gas explosion caused an “inferno” to erupt at a block of flats in Bedford.
Bedfordshire Police Chf Supt John Murphy said it is possible more deaths will be discovered in the coming days as emergency services search the scene.
Two people were seriously injured, one died, and a firefighter suffered smoke inhalation after the explosion, the force said.
“Very sadly we know that at least one person has passed away in the explosion today,” Mr Murphy said.
“There is a possibility that there will be more fatalities discovered in the coming days as we continue to search through the scene and a number of people, as my colleague from the fire services has identified, were injured as well today.”
Local residents have been urged to avoid the area and keep doors and windows closed.
Retired photographer John O’Reilly, who lives in a block of flats adjacent to the block where the fire was, said the blast knocked him off his feet and there were bricks strewn across the road.
The 76-year-old, speaking at a police cordon along the road from the flats, said: “There was a loud explosion which knocked me off my feet.
“I got dressed and walked out into the road and walked out into the road to find the adjacent block on fire.
“There were bricks in the road so it was obviously a very large explosion to do that sort of damage.”
He said he did not know when he would be allowed back into his property.
Adam Fisher, a 37-year-old sales worker whose office is nearby, said he heard a "huge explosion" before witnessing "an inferno" at the site and people screaming.
"A huge explosion heard - everyone went to our work car park to see what was happening," he said,
"Our building is adjacent to the apartment complex - immediately an inferno (was) visible, huge smoke cloud billowing, people screaming and people frantically calling for emergency services."
Mr Fisher shared footage on Twitter which shows plumes of flame erupting from the building as fire engines showered the blaze with water.
The fire service said in a statement: "Bedfordshire Fire and Rescue Service are currently in attendance at a major gas explosion on Redwood Grove, Bedford.
"There are currently six appliances, two water carriers, an incident command unit at the scene.
"Please avoid the area and keep windows and doors closed."
Police, fire and ambulance service all attended the scene.
“(The fire) has engulfed the whole building and caused a large portion of the roof to collapse,” it said in a statement.
“An emergency assistance centre has been set up by Bedford Borough Council, at the John Bunyan Centre in Bedford, for people who have been evacuated and need support.
“An adjacent block of flats has also been evacuated and we are working as quickly as we can to get people back into their homes as quickly as possible.”
A nearby primary school has been evacuated as a result of the fire on Redwood Grove.
Andy George, headteacher at Shackleton Primary School, said: “Following the fire in the Redwood Grove area of Bedford earlier today, pupils at Shackleton Primary have been sent home due to the school’s proximity to the incident.
“All children are safe and the school is working with the emergency services. The school expects to re-open tomorrow.”