Ten fire engines and around 70 firefighters were called to a fire at a shop with flats above on Walworth Road in Walworth.
The ground floor of the building was destroyed by the blaze and a small part of the basement, first floor and second floor were also damaged.
Firefighters wearing breathing apparatus rescued one man and one woman from a first floor flat roof using a short extension ladder. The woman was treated at the scene for smoke inhalation then taken to hospital by London Ambulance Service crews. A further six people left the property before the Brigade arrived.
Station Manager Pete Cox, who was at the scene, said: "When crews arrived they were faced with a lot of thick, black smoke.
"Firefighters worked hard to bring the fire under control."
Walworth Road remains closed.
The Brigade was called at 0742 and the fire was under control by 0945, but crews will remain on scene throughout the morning damping down. Fire crews from Old Kent Road, Lambeth, Peckham, Dowgate, and surrounding fire stations are at the scene.
The cause of the fire is under investigation.