Six fire engines and around 40 firefighters attended a fire at a business park on River Road in Barking.
Part of a multi-purpose single-storey industrial unit was damaged in the fire. No injuries were reported.
The Brigade's Fire Investigators believe the fire was caused by the self-heating of oil soaked paper towels.
A London Fire Brigade spokesperson said: "Natural fibres, such as cotton found in cloths, are susceptible to spontaneous heating and self-combustion. When this is mixed with materials such as oils or cleaning products, the likelihood of a fire increases as temperatures can build up to a point where the material smoulders and eventually ignites.
"When using oils and cleaning products with cloths, make sure you wash them at the right temperature with the appropriate detergent to remove any oil based contaminants.
“Also make sure you wait for your laundry to cool down before packing it away and store it in a well ventilated place.”
The Brigade was called at 0230 and the fire was under control by 0414. Fire crews from Barking, East Ham, Plaistow, Ilford and Dagenham fire stations were at the scene.