An early-morning apartment fire in Penetanguishene sent residents outside in frigid conditions Monday as authorities launched an investigation into what police describe as suspicious circumstances.

Emergency crews were called shortly after 7 a.m. to a multi-unit building on Poyntz Street. Firefighters quickly contained the flames in a third-floor unit, while police assisted with evacuating occupants from the building.

One apartment suffered significant damage, but no injuries were reported. Most residents have since returned to their homes, with the exception of those displaced by the fire.

The Office of the Fire Marshal is investigating the cause, and no charges have been laid. Police are asking anyone with relevant information to contact the OPP.