One person has died and three others were taken to hospital after a "major gas explosion" and a huge fire at a block of flats in Bedford.
Bedfordshire Police said further bodies could be found in the coming days after 20 flats were engulfed in flames in Redwood Grove.
Eyewitnesses described hearing an explosion at about 09:30 BST.
The fire service said an investigation was under way and more details would become known in the coming days.
Ch Supt John Murphy said: "Very sadly we know that at least one person has passed away in the explosion today.
"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."
Adrian Mazurkiwicz, who lives in a top floor flat in a three-storey block adjoining the one where the explosion happened, said he saw two people jump from windows to escape the blaze.
He told how on hearing the explosion, he and his partner rushed to "start knocking on people's doors to get everybody out, and then when I was outside the building I saw the walls being torn apart... and all of the windows out, and smoke and flames pretty much instantly".
"I saw a couple of people jump out of the building and started helping them out... bringing them away from the fire, away from the danger, but it was a very, very serious and very big explosion," he said.
Mr Mazurkiwicz's flat has been destroyed in the blaze.
He said he hoped his neighbours in the building were all "OK".
"We saw people jumping out from the flat that was directly affected," he said. "I think that was the flat that blew up, and that was where the gentleman jumped out and hurt his hip really badly - we pulled him away.
"And then I saw another gentleman on the other side of the building - seems like he's just been blown out of the window by the whole explosion."
He added: "The walls [of the building] have just been completely cracked like a walnut - there's been so much debris flying out of everywhere - ashes, smoke, dust, fire - just instantly everywhere - blazing out of the windows - and that's why people started to jump out."
An emergency centre has been set up at The John Bunyan Centre in Bedford for evacuees and those needing support, police said.
Bedfordshire Fire and Rescue Service said the fire was caused by a "major gas explosion" and urged people to keep doors and windows closed.
Witness Alex Feltham said after hearing the "boom" the block of flats became "a raging inferno".
Another witness, Adam Fisher, described "a huge explosion".
"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."
A block of flats next to the three-storey block where the explosion happened has also been evacuated, and police said they were "working as quickly as we can to get people back into their homes as quickly as possible".
Dezso Balazs lives in a neighbouring block of flats.
"I heard a big noise like an explosion and then I grabbed my family and we came out and we saw the next flat block on fire. Part of the building had been blasted out. Everybody started to panic and run around.
"Everybody just looked after their loved ones and other people to make sure everybody was all right."
A nearby primary school was also been evacuated.
Andy George, head of 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."