The fire was in Rhodes Tce, about 10.35pm.
Crews found the fire "well involved" when they got there, Fire and Emergency New Zealand said.
Police were called because there were initial concerns there may have been people at the property.
However, the occupants were later located safe and well, a police spokeswoman said.
There was no indication the fire was suspicious, but a scene guard was in place overnight and inquiries were ongoing, she said.
North East Valley resident Laura Hudson said the sound of many sirens going down North Rd got her out of bed to the "terrible sight of flames in the valley".
"There must have been at least eight emergency vehicles responding. It was a relief when the flames finally subsided."