Four fire engines and around 20 firefighters and officers were called to a fire at a maisonette in Albert Road in Leyton.
A first floor maisonette was completely damaged by fire. Part of the roof was also damaged in the blaze.
Two adults and two children left the property before the arrival of the Brigade. One man was treated at the scene by London Ambulance Service crews before being taken to hospital.
The Brigade was called at 1231 and the fire was under control at 1407. Fire crews from Leytonstone, Walthamstow, Stratford and Homerton fire stations attended the scene.
The cause of the fire is under investigation.