Senior Constable Hurley said he did not want to speculate about what went wrong but said it was the first crash of its kind he had attended in the Wanaka area in more than 10 years.
Chief Fire Officer for the Hawea Volunteer Fire Brigade Doug Brenssell said the vehicle had come from a driveway above Charles Court.
It ran down a steep empty section; across Charles Court; through a section, narrowly avoiding a large boat on a trailer; smashed a wooden boundary fence; crossed a front lawn and a sandpit; took out a veranda post; and crashed cleanly through the double aluminium ranch sliders.
The vehicle ended up inside the lounge, shunting a lounge suite and clothes rack across the room.
A volunteer firefighter managed to start the vehicle, and drove it back out on flat tyres.
Mr Brenssell said several volunteers were builders and they quickly cleared the debris and boarded up the damaged door to enable the family to remain in the house last night.