Ten fire engines and around 70 firefighters were called to a fire at a block of flats on Hillingdon Street in Walworth.
A flat on the 11th floor of a 17-storey building was destroyed by fire. Three people were assessed on scene by London Ambulance Service crews and one woman was taken to hospital.
Station Commander Tony Perks, who was at the scene, said: "This was a very visible fire, and the area became increasingly busy as a result.
"People are advised to continue to avoid the area at this time, while crews damp down remaining hot spots."
The Brigade received the first of around 70 calls at 1355 and Control Officers mobilised crews from Dowgate, Dockhead, Soho, Whitechapel and surrounding fire stations to the scene. The fire was under control by 1454.
The cause of the fire is under investigation.