Twenty fire engines and around 125 firefighters tackled a fire at a factory on Minerva Road in Park Royal.
Most of the ground floor and half of the roof of a single-storey industrial bakery was damaged by fire. There were no reports of any injuries.
Eleven gas cylinders were removed as a precaution as some cylinders can explode when exposed to heat.
Station Commander Paul Morgan, who was at the scene, said: "Firefighters were faced with a fully-developed fire on arrival.
"Three people left the building before the Brigade arrived uninjured.
"Crews worked incredibly hard to contain the fire to the single-storey building and prevent further damage. The blaze produced some smoke and we asked residents in the local area to keep their windows and doors closed.
"One of the Brigade's 32-metre turntable ladders was used as a water tower to get water on to the building externally. Firefighters also used one of our drones to provide an aerial view and support observational awareness.
"There was a cordon in place as a precaution and Minerva Road was closed."
The Brigade was called at 0323 and the fire was under control by 0610. Fire crews from Park Royal, Willesden, Wembley, North Kensington, Ealing, Chiswick and surrounding fire stations attended the scene.
The fire is believed to have been accidental and caused by a flat bread that ignited within an oven, this then progressed onto the conveyor belt and ignited the belt.