Five fire engines and around 35 firefighters were called to a flat fire at Honour Gardens, Dagenham.
Half of a three roomed flat in a seven-storey apartment block was destroyed by fire.
One person left the building before the Brigade arrived and one person was led to safety by firefighters. Two people were treated on scene, one of whom was taken to hospital by London Ambulance Service.
The Brigade's Control Officers received the first of five calls at 1155 and mobilised crews from Dagenham, Ilford, Barking and surrounding fire stations to the scene. The fire was under control by 1408.
The cause of the fire is under investigation.