Firefighters and two helicopters were called in to help fight the fire, after a controlled burn-off got out of control about 2.40pm in Meyers Pass, which links the Hakataramea Valley and Waimate, near Kurow.
A Fire and Emergency New Zealand spokesman said the fire had been fanned by a nor-westerly wind coming over the pass, but the terrain was the biggest challenge.
The Meyers Pass has an elevation of 700 metres.
No structures were threatened by the fire.
The farmer had called emergency services after the burn-off on his land got out of control.
Nine fire appliances from Timaru, Waimate, Cave, Kurow, Otematata, Waihaorunga and Glenavy attended, including tankers, pumps and a command unit.