Media playback is unsupported on your device Media caption State policeman, Tom Pinkerton, said the father 'immediately rushed back to the house' but was too late

Seven children, aged from seven months to 11 years old, have died in a fire at a farmhouse in the borough of Blain in the US state of Pennsylvania.

The children's mother was milking cows in a barn and their father was napping in a delivery vehicle when the fire took hold, a state trooper said.

A girl, three, who survived the fire, alerted her mother to Tuesday night's blaze, Trooper Tom Pinkerton said.

Fire officials are investigating the cause of the blaze.

The children - six girls and one boy - died of smoke inhalation, police said the Perry County coroner had ruled.

The children's grandfather, Noah Sauder, told the Associated Press he believed the fire had started in the kitchen, ignited by a propane gas heater.

'Daughter comes running'

News organisations identified the parents of the children as Theodore and Janelle Clouse, who owned the dairy farm where the fire occurred.

Police said Theodore Clouse left to begin a round of milk deliveries late on Tuesday, then parked the truck about a mile from the farm and dozed off.

"While mom's milking cows, her three-year-old daughter comes running into the barn and the three-year-old tells the mother that there's smoke inside the house," Trooper Pinkerton said. "Mom leaves the barn, comes running out, sees that the house appears to be on fire."

The mother ran to a neighbour to alert emergency services and ran with the child to the father's truck, the Associated Press reported the trooper as saying.

The father rushed back to the house, at which point the house was fully engulfed in flames and the fire department had begun to battle the blaze.

The house is one of a cluster of homes near a road junction in Blain, a stretch of farm land about 20 miles (32km) north of Harrisburg.