Twenty fire engines and around 125 firefighters tackled a fire at an industrial estate on Walmgate Road in Perivale.
Half of a range of single and two-storey warehouses were damaged by fire. There were no reports of any injuries to members of the public.
Assistant Commissioner Paul McCourt, who was at the scene, said: "This was an aggressive, challenging, and incredibly complex fire located inside an industrial estate premises that contained a number of small businesses within the same building. Firefighters worked incredibly hard throughout Christmas Day to bring the fire under control and protect adjoining property and businesses.
"More than 125 firefighters attended the scene and the Brigade used 32m and 64m turntable ladders as water towers to put the fire out. Six firefighters were assessed for injuries and three were taken to hospital. I am pleased to confirm that they have all since been discharged. Crews remained on the scene through the night and on Boxing Day to fully extinguish the fire and will stay at the scene to dampen down remaining hotspots.
"The fire was severe, producing heavy smoke that was being carried by the wind onto nearby housing. Working with our blue light partners, the Brigade informed the local community to keep windows and doors closed and avoid travelling within the smoke affected area.
"The Brigade’s 999 Control Officers took more than 40 calls to this incident. Whilst this was a significant fire occurring on a public holiday, Control Officers ensured that fire appliances were strategically relocated across London so that emergency cover was retained to provide a service within our normal six and eight minute response standards."
The Brigade's 999 Control Officers received 44 calls about the incident. The Brigade was called at 1235 and the fire was under control by 1952. Crews from Wembley, Northolt, Ealing, Park Royal and surrounding fire stations attended the scene.
The cause of the fire is under investigation.