Firefighters were called to the former Young Partnership Ltd timber yard at Kaihiku, about 15km west of Clinton, shortly before 4pm yesterday.
Three appliances, three tankers and volunteer firefighters from Balclutha, Clinton, Clutha Valley, Tapanui, and Waiwera South attended the blaze.
Waiwera South Volunteer Fire Brigade Chief Fire Officer Maurice Walter said a stubble fire spread to a stack of straw, through trees and on to a shed and stacks of timber.
Mr Walter said it took about 20 firefighters, some using breathing apparatus, an hour to get the blaze under control, and firefighters remained at the scene for several hours.
Clutha Rural Fire duty officer Mike Harris said farmer and owner of Young Partnership Ltd Eion Young had ''misinterpreted'' the rules around what fires were allowed during a restricted fire season.