A father and five young children are believed to have died when a blaze ripped through a farmhouse in Powys.
Dyfed-Powys Police said the children, aged between four and 11, were killed in the fire at the remote property at Llangammarch Wells.
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."
Chris Davies, Brecon and Radnorshire MP, said: "I am absolutely devastated at the news that there was an overnight fire in Llangammarch Wells, which has claimed the lives of a father and his young children.
"As a father to two young girls, this news has shocked me to the core. My thoughts are with the family and local community at this terrible time.
"Our local emergency services were on the scene swiftly and have worked hard to put out the fire and identify who has been hurt. I will be keeping in close contact with the emergency services over the next 48 hours."
See full story in the County Times