Firefighters battled a house blaze late Tuesday afternoon in Wasaga Beach.
Crews knocked down the flames quickly, extinguishing hot spots.
The fire chief told CTV News the structure on River Road East was vacant at the time and slated to be torn down.
There is no estimate of the damage at this point.
The OPP has been called to investigate any possible foul play after witnesses reported seeing someone running from the scene.
The section of River Road East was closed for firefighters to work. It has since reopened.