Ten fire engines and around 70 firefighters were called to a fire at an electrical substation on Castor Lane in Poplar.
Part of the ground floor of a two-storey electrical substation was damaged by fire. Around 100 people were evacuated from an adjacent depot and 1500 students were evacuated from a college at the rear of the substation.
Station Commander Colin Digby, who was at the scene, said: "Firefighters worked hard in challenging conditions to bring the fire under control.
"The fire caused power outages in the area, affecting around 4,500 customers."
The Brigade was called at 1248 and the fire was under control by 1802. Fire crews from Shoreditch, Bethnal Green, Shadwell and Plaistow fire stations were at the scene.
The cause of the fire is believed to have been electrical.