Calgary fire investigators are working to determine what sparked a blaze in the community of Woodlands on Sunday.
Firefighters were called to a multi-family complex in the 500 block of Woodridge Terrace Southwest at around 8:30 p.m.
Crews found thick black smoke and large flames coming from the window of one of the second-floor units.
Firefighters worked to extinguish the blaze from the outside of the building before entering the unit and putting out more flames in a bedroom.
The Calgary Fire Department said all four occupants were able to get out safely thanks to working smoke alarms that alerted them to the fire.
No injuries were reported and the fire department said crews were able to keep flames from spreading to other units.