Ten fire engines and around 70 firefighters responded to a fire on Copley Close, Hanwell.
The fire was located in a block of flats consisting of five floors. A split-level flat on the third and fourth floors was alight. There are no reports of any injuries at this time.
Traffic in the surrounding area is likely to be impacted as crews remain on scene into the evening.
The Brigade received over ten calls reporting the fire, with the first call taken at 1815. Control officers mobilised crews from Ealing, Southall, Wembley and surrounding fire stations to the scene. Firefighters were able to bring the incident under control by 1942.
The cause of the fire is under investigation by the Brigade's Fire Investigation Team.