Four fire engines and around 25 firefighters rushed to the ground floor of a block of flats on fire in Apple Grove Estate, Harrow on Friday.
Prior to the Brigade arriving, a woman and three children fled the building and were treated by London Ambulance Service.
“Part of the external fascia of the building, from ground to first floor, was damaged by fire, as well as a small amount of two flats. An external storage cabinet was destroyed.
“A woman and three children left the building before crews arrived and were treated on the scene by London Ambulance Service crews as a precaution.
“The Brigade was called at 1544 and the fire was under control by 1734. Fire crews from Wembley, Northolt and Stanmore stations attended the incident.
“The cause of the fire is believed to be the unsafe disposal of smoking materials.”