Fifteen fire engines and around 100 firefighters tackled a flat fire on Mavis Grove in Hornchurch.
Two second floor flats were destroyed by the blaze and part of the roof were damaged. Around 60 people were evacuated from the building before the Brigade arrived. One woman was taken to hospital by London Ambulance Service crews.
The Brigade was called at 0055 and the fire was under control by 0402. Fire crews from Hornchurch, Harold Hill, Romford, Wennington and surrounding fire stations were at the scene.
The cause of the fire is under investigation.