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Two people have been confirmed missing after a fire at a four-storey block of flats in which a person died.
The blaze engulfed the building in Rowe Court, Reading, in the early hours of Wednesday.
Police said they did not anticipate any more survivors from the fire, despite "an extensive search".
A 31-year-old man arrested on suspicion of murder and arson remains in police custody.
Thames Valley Police said it had obtained a warrant for further detention, giving detectives more time to question the man.
Twenty people are believed to have been unable to return to their homes, with seven placed in emergency accommodation by the council.
Emergency services are set to start assessing the structural damage to the building, before recovering people from inside.
Supt Steve Raffield, of Thames Valley Police, said: "We've been working alongside our partner agencies to do everything we can to find signs of life.
"Sadly, it's highly unlikely we'll find any further survivors in the building."
He added the block of flats was "unstable".
The fire, which is not being treated as terrorism related, started at about 03:00 GMT on Wednesday.
The Royal Berkshire Fire and Rescue Service said its crews were at the scene within eight minutes.
Four people were treated in hospital while another seven received medical care from ambulance crews.
Although the cause of the fire is believed to be arson, its source has yet to be found.
Speaking to BBC Radio Berkshire, Marius Hopley, from the Rotary Club of Pangbourne, said his group had been providing displaced families with clothes and toiletries.
He said: "Think of what you're standing in now - we needed to provide that stuff.
"They have everything they need at the moment to get them through the next three days at least."
The organisation has set up a donation link via its Facebook page.
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The Right Reverend Dr Adam Carlill said St George and St Mary Magdalen Church was opened as a rest space on Wednesday to emergency crews, and would remain open on Thursday.
"To have a building where you can just go in, sit and be quiet and reflect... I think is vital," he said.
Homeless charity New Beginnings Reading took clothing and toiletries to English Martyrs Catholic Church for families displaced by the fire.
Centre manager Louis Howard-Krelle said: "I can only imagine how absolutely awful it must be to lose absolutely everything just before Christmas.
"Thankfully here we actually provide Christmas hampers for those who can cook at home, as well as brand new presents for those who might be in a bit of need at this of year as well."
The centre is appealing for further donations of toiletries, coats, jumpers, trousers, underwear and socks.
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