Four fire engines and around 25 firefighters were called to a house fire on Boundfield Road in Catford.
Half of the first floor of an end-of-terrace house was damaged by fire. A woman was taken to hospital by London Ambulance Service crews.
The fire is believed to have involved a candle.
A London Fire Brigade spokesperson said: “It’s really important that you never leave candles unattended and keep them away from anything that could catch fire such as curtains, furniture or clothes.
"We recommend swapping traditional candles for LED flameless ones as they are much safer, but if you do use real candles, follow our simple safety tips."
The Brigade was called at 0209 and the fire was under control by 0312. Fire crews from Lee Green, Lewisham and Bromley fire stations attended the scene.