Thunder Bay Fire Rescue was called to an incident on the city's south side.
Around 9:15 p.m. on Tuesday, TBFR responded to a structural fire at an apartment complex on Cumming Street.
When they arrived, firefighters discovered dense smoke that was concentrated on the first floor and was spreading to the second.
A fire in a basement area kitchen was quickly located by the crew and extinguished.
Responders learned that the fleeing occupant used an extinguisher, which helped slow the spread of the flames.
Firefighters determined that unattended cooking was the cause.
High-volume fans pushed the smoke out of the rest of the building, and residents were allowed to return to their apartments afterwards.
The lone occupant was treated by Superior North EMS for smoke inhalation.
A total of six pumper trucks, one aerial ladder and one command vehicle were dispatched to this location.
TBFR reminds the public not to leave cooking unattended, as this contributes to a high percentage of home fire incidents in Ontario.