Eight fire engines and around 60 firefighters were called to a fire at a coffee shop on the High Street in Harlesden.
A basement kitchen was destroyed in the fire. Three people left the property before the Brigade arrived. There were no reports of any injuries.
Station Manager Lucy Macleod, who was at the scene, said: "We closed the High Street from the junction with Park Parade and Nightingale Road, so there was a lot of traffic in the area as it's a main thoroughfare.
"We advised drivers to avoid the area if possible."
The Brigade was called at 1240 and the fire was under control at 1425. Fire crews from Willesden, Park Royal, North Kensington, Acton and surrounding fire stations attended the scene.
The Brigade's fire investigation team believe the most likely cause of the fire was an issue with a lithium battery, either from metal touching the contacts or from mechanical damage.