It took seven fire crews, three water tanks and heavy machinery to tackle the farmhouse fire in the small Waipango community.
And nearly half a day later, firefighters had "not even started on the inside of the house".
In just minutes, the farmhouse had burst into flames and thick layers of black smoke billowed from its roof across the rural settlement near Riverton about 11am yesterday.
Fire Risk Management Officer Murray Milne-Maresca, of Invercargill, said firefighters who came from across the region had not, late yesterday, managed to get inside the scorched property, after hours of cooling down its foundations.
"We won't know for a while what caused the fire. We're still in the preliminary stages of the investigation because the house is very big.''