Eight fire engines and around 60 firefighters tackled a fire at a builders' storage unit on Barking Road in Plaistow.
Most of the storage facility was damaged by the blaze. Two women were treated on scene by London Ambulance Service crews after suffering from smoke inhalation.
Station Commander Jason Oliff, who was at the scene said: "Firefighters worked extremely hard in arduous conditions to bring the blaze under control. The fire produced a lot of thick black smoke so we asked local residents to close their doors and windows."
The Brigade was called at 0917 and fire was under control by 1106. Fire crews from East Ham, Stratford, Barking, Leytonstone and Millwall fire stations were at the scene.
The Brigade's Fire Investigators believe the fire was accidental and involved an electrical supply.