Helicopters were used to put out a fire with a 300m front in scrub near the snowline of the Big Ben Range in Canterbury.
The fire service was alerted shortly before 10am on Saturday after police received a report of an explosion in the inaccessible area.
It was believed a light aircraft may have crashed but this turned out not to be the case, Southern fire communications shift manager Andrew Norris said.
Ground crews couldn't reach the fire 1600m up the mountain range so the Department of Conservation used helicopters to fight it.
"We don't know the cause of the fire but it has been contained and extinguished by DOC using two helicopters," Mr Norris said.
The fire was on DOC land and High Peak Station was used as a base for operations.