Twenty firefighters and five appliances from three stations — Runanga, Cobden and Greymouth — spent more than two hours battling the Carroll St fire, after the alarm was given just after 9.30pm.
Runanga Volunteer Fire Brigade Deputy Fire Chief Aaron Sheehan said the house was fully involved when the brigade arrived, and they immediately set about protecting neighbouring property and carrying out an exterior fire attack on the burning house.
Entry was impossible because of the intense heat.
Even the lawn was on fire.
Firefighters had to remain at a safe distance as walls of the house began collapsing, DFC Sheehan said.
The neighbouring garage was saved, but suffered some minor damage as the spouting melted, he said.
Nobody was home at the time and there were no pets.
Police talked to the owner of the house.
Mr Sheehan said there was no indication of cause, and a fire investigator was at the scene on Thursday morning.
"There is a little bit of the front left, but nothing much else."