Firefighters battled a large fire in gale force winds in central Warragul on Sunday night.
Police said the blaze, which destroyed a vacant commercial building in Napier St, was reported just after 8pm.
It is the third fire reported at the building near Club Lane in the space of 10 days.
At least 11 CFA units attended the scene to extinguish the fire, with smoke covering most of the Warragul central business district.
Baw Baw Criminal Investigation Unit detectives said the cause was unknown at this stage.
Talking to the Gazette yesterday morning, they reported the site was a crime scene and arson squad chemists were attending yesterday.
Detectives said it was too early to tell if the previous fires - reported on Friday, August 23 and Monday, August 26 - were linked to Sunday night's fire.
The first fire, occurring at 5.30pm, was allegedly ignited in a wheelie bin. It destroyed the bin and caused major damage to an internal brick wall and plaster ceiling of a room.
At the time, police said local youth frequently attended the vacant building which had considerable damage from trespassers.
Anyone with information or who noticed unusual activity in the vicinity of Napier St on Sunday night is urged to contact Warragul Police on 5622 7111.