When Whanganui firefighters arrived shortly after, the foundations were burning and they worked for more than two hours to extinguish the flames.
Whanganui fire chief Bernie Rush said it would be hard to determine the cause of a fire that was so advanced.
"It is not often that the foundations would be burned like that," he said.
Mr Goble said the house was probably built in the 1980s and had been moved on to the property in 2000 when the farm changed from dry stock to dairy.
The occupant of the house lost all his possessions in the fire and Mr Goble said he was in town buying some new clothes yesterday.
"Fortunately there is room for him to stay in the main house with me. There are places he could rent nearby but he won't have anything so he will need somewhere furnished."
Police would like to speak to anyone who may have seen unfamiliar vehicles in the area on Saturday night or Sunday morning.