The blaze erupted Monday afternoon on the city's north side.
Alex Munroe says he watched flames creep up the side of the garage and engulf the house, and he says he heard some big booms and glass breaking as the fire spread quickly.
Assistant fire chief Curtis Bossert of Kamloops Fire Rescue says a fuel tank on a vehicle in the garage may have fed the flames and that the house is severely damaged.
Bossert says an ambulance took the only person who was at the home and was suffering from smoke inhalation to hospital.
The homeowner, who identified herself only as Linda, says her daughter, son-in-law and two grandchildren aged six and 12 live in the house.