Investigators with the Ontario Fire Marshal’s office and the OPP are trying to determine what caused a house fire near Muskoka Airport.

A driver traveling north on Hwy 11 just after 2 a.m. Saturday spotted the blaze on Gravenhurst Parkway, and called 911.

Crews arrived to find the single-family detached home engulfed in flames. Its roof and walls had already begun to collapse.

It took nearly 20 firefighters several hours to get the flames under control, and to extinguish the hot spots.

Jason Williams, an investigator with the OFM, tells CTV News the home was undergoing renovations, and no one was living there at the time of the fire.

Investigators were on scene all day Sunday. They had begun the excavation process, and were sifting through debris in hopes of determining the origin and cause of the fire.

Williams says the home did not have working smoke alarms, and he does not believe the property owner had insurance.

So far, the OPP have not laid any charges, but they’re not ruling out a suspicious cause.