People are staying warm on a Barrie City bus after a fire in one unit forced the evacuation of a building at 139 Wellington Street.

The Barrie Fire Department says the fire broke out in the living room of a second floor unit, but was contained by the 20 firefighters who responded.

No one was in the unit at the time of the fire, but four cats were rescued.

Fire crews have to clear the building of smoke before people can return to other units in the building.

The exact cause and amount of damage has not yet been determined.