Four fire engines and around 25 firefighters attended a fire at a block of flats on Ellis Road in Coulsdon.
Half of a second-floor flat was damaged by fire. One woman was taken to hospital by London Ambulance Service.
The Brigade received the first of three calls at 0342 and Control Officers mobilised crews from Purley, Wallington, Croydon and Mitcham fire stations to the scene. The fire was extinguished by 0412.
The fire is being treated as accidental and believed to have been caused by items left on a cooker hotplate.