One man and five children aged between four and 11 are believed to have died in a fire which ripped through a farmhouse in Llangammarch Wells, Powys, Dyfed-Powys Police said.
The blaze that occurred shortly after midnight on Monday is being treated as “unexplained”.
David Cuthbertson, 68, was named locally as the man who lived at the property with his nine children.
Three children aged three, 12 and 10 managed to escape and are currently being treated in hospital. Their injuries are not thought to be life-threatening and they have been informed of developments.
Superintendent Jon Cummins, said in a statement: “Based on current information available to us, we are working on the hypothesis that one adult male and five children, aged between 11 and four 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.
“Specialist scientists and fire investigators continue to assess the scene, which is very complex and perilous.”
Neighbours Ron, 73, and Rosemary Birchall, 68, said they were “absolutely devastated” at the news.
Ron added: “I knew him as a good father and a gentle fella. My wife would say he was an exceptional father.
“All the other villagers are upset by this because Dave has been in the village for about 15 years.”
The farmhouse is located almost a mile from a main road meaning emergency services had difficulty reaching the fire.
County councillor Tim Van-Rees, said. “I knew the father and several of the children
“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.”