Three fire engines and around 15 firefighters were called to a flat fire on Widmore Road in Bromley.
Part of a flat on the third floor of a four storey block of flats was damaged by fire.
One man, a woman and a child left the property before the Brigade arrived. They were taken to hospital by London Ambulance Service and were suffering from smoke inhalation.
The Brigade's 999 Control officers were first called at 0710 and mobilised crews from Bromley and Beckenham fire stations. The incident was under control by 0746.