Fire crews were called to a controlled burn in the Coal Stream area, south of Fairlie, and discovered the blaze had escalated to a third-alarm fire.
The 111 call came through at approximately 5am, according to Fire and Emergency shift manager Ryan Dawson.
A firetruck and two tankers initially headed to the scene before calling an additional two trucks, five tankers, a smoke chaser and two senior officers to the scene.
The blaze is mostly contained, Dawson said, but additional resources were sent to assist as the wind was picking up in the area.
There was no risk to members of the public during the event.
A Fairlie resident living nearby told the Herald it was clear the fire was well under control by responding fire crews.
He said the fire covered about a hectare.
"They were knocking some trees down there, so I imagine they’re probably burning them and it’s got out of control," he said.
The town of Fairlie is inland between Ashburton and Timaru.
The fire itself was on a rural section of farmland.
