The owners of property along Whanganui's River Road watched as their house burnt to the ground with firefighters unable to cross the river to get to it.
Two fire crews were sent to the scene around 10.30pm on Tuesday evening but had no chance in fighting the blaze.
Whanganui Fire station officer Jes Sorensen said his colleagues were unable to gain access to the property as the old house was situated on the opposite side of the river towards the Gentle Annie lookout point.
"By the time the crews got there they spilt the trucks up and one truck went up the river road and a tanker and a ute went up the other side but there was no access to that side so they came back and the truck that went up the river road talked to the owners and by that time it was pretty well on the ground," he said.
Sorensen said the house was unoccupied at the time the fire started and the owners did not receive any injuries from the blaze.
A Fire and Emergency New Zealand spokesman confirmed a fire investigator had carried out an investigation into the cause of the fire and currently the fire was not being treated as suspicious.