Volunteer firefighters from Clutha Valley and Balclutha were called to a dairy farm in Paisley Rd at 1.20am. A water tanker from Tapanui also attended.
Detective Constable Robin Hutton, of Balclutha, and specialist fire investigator Paul Glanville, of Invercargill, spent several hours examining the scene yesterday.
Det Const Hutton said the cause of the fire had not been determined and it was not yet known where the blaze began.
The fire was being treated as suspicious, he said.
A six-bay shed, a two-bay shed and a small barn were ''absolutely destroyed'' in the blaze, which took firefighters about five hours to subdue.
The fire happened on a 214ha dairy farm about 11km from Clydevale, owned by Paul and Karen Tunnah.
Police were seeking sightings of vehicles or people acting suspiciously in the Wharetoa area near Clydevale between midnight and 5am yesterday.
Those with information should call Balclutha police on (03) 418-0203 or anonymously through Crimestoppers on 0800 555-111.
