Six fire engines and around 40 firefighters tackled fire in a waste and recycling plant in Wallingford Road, Uxbridge.
Mixed paper and card weighing 120 tonnes – equivalent to the average weight of a blue whale - was alight.
Station Manager Pete Clark who was at the scene said: “This was a very deep seated fire and crews worked very hard to bring it under control."
The Brigade was called at 0502 and the fire was under control by 1126. Fire crews from Hillingdon, Hayes, Southall, Northolt and Ruislip fire stations were the scene.
The cause of the fire is under investigation.