The LFB has said its investigation team believe the fire was started accidentally, caused by the failure of a lithium battery. They also said three people left the building before they arrived on the scene.
Firefighters from East Ham, Plaistow, Stratford and surrounding fire stations were at the scene.
The brigade has said on X (formerly Twitter) that although the fire was now under control, traffic in the area would be impacted as crews remain on scene.