Twenty fire engines and around 125 firefighters were called to a blaze at a warehouse in Barking, east London.
The London Fire Brigade (LFB) attended the single-storey warehouse on Alfreds Way on Friday evening after reports of a building being alight.
Crews from Barking, East Ham, Dagenham, Plaistow, Ilford and surrounding fire stations also attended.
The LFB said the fire was under control at around 01:00 BST on Saturday.
Station Manager Jim Smith, who was at the scene, said: “On arrival crews were faced with a well developed fire and large clouds of smoke.
“Crews worked hard to prevent the fire spreading.
“Firefighters expect to be on scene throughout the morning.”
The fire service said the cause of the blaze was not known at this stage.