Six fire engines and around 40 firefighters were called to a flat fire on Edgware Road in Colindale.
Part of a five-roomed flat on the third floor of the building was damaged by fire. There were no reports of any injuries. A woman and a child were assessed on scene by London Ambulance Service crews.
The Brigade’s 999 Control Officers took 22 calls to the fire.
Station Officer Peter Shaw, who was at the scene, said: “As we arrived, the kitchen and the balcony of a flat on the third floor was fully alight and producing a large amount of heavy smoke.
“Everyone was out of the building on arrival and crews got to work incredibly quickly to bring the fire under control.
“The fire was beginning to spread into the loft space, but firefighters quickly contained the fire, saving the roof of the building.
“There were no working smoke alarms fitted inside the property and the occupants were alerted to the fire after smelling burning. Smoke alarms give the earliest possible warning when a fire starts and we would urge everyone to make sure they have one fitted in every room where a fire can start and a heat alarm in the kitchen.”
The Brigade’s Fire Investigators believe the fire was accidental and caused by the unsafe disposal of smoking materials.
The Brigade was called at 2049 and the fire was under control by 2155. Fire crews from Stanmore, Harrow, Park Royal, Northolt, Barnet and Hornsey fire stations attended the scene.