Update 2.45pm: A father and five young children are believed to have died when a blaze ripped through a farmhouse in rural Wales.
Dyfed-Powys Police said the children, aged between four and 11, were killed in the fire at the remote property at Llangammarch Wells, Powys.
A neighbour raised the alarm shortly after midnight on Monday and three children, aged 13, 12, and 10, managed to escape unharmed.
The man who died has been named locally as David Cuthbertson, who was known as Dave and thought to be in his 60s, and neighbours said he "doted" on the children.
Superintendent Jon Cummins, of Dyfed-Powys Police, said: "Based on current information available to us, we are working on the hypothesis that one adult male and five children, aged between four and 11 years old, are unaccounted for and believed to be deceased within the house.
"Due to the severity of damage at the scene we are unable at this stage to identify any of the deceased."
Mr Cummins said the cause of the fire was being investigated but currently remained "unexplained".
"Dyfed-Powys Police is continuing to investigate and deal with the tragic house fire that occurred at Poityn Farm, Llangammarch Wells, Powys, shortly after midnight on Monday October 30," he said.
"Specialist scientists and fire investigators continue to assess the scene, which is very complex and perilous.
"The 13, 12 and 10-year-old children that managed to escape remain in hospital. None are in a life-threatening condition, and they are being supported by specialist officers and family."
The officer's statement continued: "At this time we are treating the cause of the fire as unexplained.
"The family are our priority and they are being kept informed and fully supported by specialist officers.
"They have asked that their privacy is respected at this extremely difficult and traumatic time and do not wish to be contacted in any way.
"They would also like to thank friends and locals for their support, sympathies and all kindness shown to them.
"Our officers and all our partners such as the fire service are working in extremely challenging conditions and circumstances, and I thank and commend them for their efforts.
"This is a tragic incident, and our deepest sympathies are with the family and all those affected."
Earlier: A fundraising page in support of a family whose father is believed to have died in a fire at a farmhouse in rural Wales has raised almost £2,500 (€2,800).
Well-wishers have left donations totalling £2,495 on a JustGiving page just a day after the tragedy at a remote property at Llangammarch Wells, Powys.
David Cuthbertson, who was known as Dave and thought to be in his 60s, is feared to be among those to perish in the fire, alongside several members of his family.
Police said there had been fatalities but due to the severity of the damage they were unable to confirm how many people had been killed.
Media reports suggest four of his children died in the fire.
A message on the JustGiving site says: "I'm sure any small donation will help them massively."
Other tributes read "Very sad. Special thoughts are sent to family and friends...x" and "So sad. R.I.P. x".
A neighbour raised the alarm shortly after midnight on Monday and three children, aged 13, 12, and 10, managed to escape unharmed, but police say "a number of people" are missing.
Ron Birchall, 73, who lives at the former Aberceiros Inn in the village, said: "He (Mr Cuthbertson) was a great guy.
"All I can say is that he was a great father who loved his kids and doted on them."
Mr Birchall said he had known Mr Cuthbertson since he first moved to the village 15 years ago.
"We have been living here since 2002 and when we arrived he was living in a village a couple of miles away and then a year or so later he moved to the village," he said.
"I used to see him walking around the village or in his vehicle. We saw the kids coming to pick up the bus to school."
Mr Birchall said he and his wife Rosemary knew nothing about the incident until they woke up in the morning - even though around 20 emergency vehicles had parked at the pub.
"The village is devastated. We didn't realise anything had happened in the early hours and we didn't know anything until we got up at 6am," he said.
Mr Birchall said Mr Cuthbertson was separated from his partner who had moved away after suffering a stroke.
County Councillor Tim Van-Rees, who represents the area, spoke of the community's shock at the devastating loss of life.
"I knew the family, not well, and I knew the father and several of the children," he said.
"They were a large family, although I am not sure how many were living there.
"It is absolutely shocking and a devastating blow and it is possibly just as well we are in half-term at the moment because the effect on our children and the schools would have been very severe."
Chief Superintendent Richard Lewis, of Dyfed Powys Police, said the three children who escaped were being treated in hospital but do not have life-threatening injuries.
"However, there are a number of people unaccounted for at this time and we can confirm that there are known to be fatalities," he said.
"Specialist scientists and fire investigators are still assessing the scene and at this time we are treating the cause of the fire as unexplained."
The fundraising page is available here.