Thunder Bay Fire and Rescue is investigating the cause of a house fire on the city`s south side.

Fire crews were called to a home on the 1300 block of Mountdale Avenue at about 10 p.m. Saturday, where they encountered large flames at the back of the one-storey building.

Officials report the fire was put out quickly, but not before it did significant damage to the home.

Everyone inside was able to escape without injury.