Five fire engines and around 30 firefighters tackled a fire by the A40 Western Avenue in East Acton.
Part of a ground floor flat at a six-storey block of flats was damaged by fire. There are currently no reports of any injuries.
The incident was by the A40 westbound, just after the junction with Old Oak Common Lane, which has resulted in heavy traffic in the area.
The fire is believed to have been accidental and caused by a candle.
A London Fire Brigade spokesperson said: “Candles are one of the most common causes of fire. It’s really important that you never leave a candle unattended and keep them away from anything else that can easily catch fire.”
The Brigade was called at 1343 and the fire was brought under control by 1436. Crews from Acton, North Kensington and surrounding fire stations have been in attendance.