Firefighters rescued a man from a fire at a flat on Breakspears Road in Brockley.
Part of a five-roomed flat on the lower ground floor of a converted semi-detached house was damaged by fire.
On arrival firefighters were faced with smoke in a communal hallway and evacuated three people from the flats. Crews tackled a fire behind a door on the lower ground floor and led a man outside who was treated on scene after suffering from smoke inhalation.
The Brigade was called at 0300 and the fire was under control by 0326. Fire crews from Lewisham, Greenwich and New Cross fire stations attended the scene.
The fire is believed to have been accidental and caused by cardboard boxes which were on top of an area with underfloor heating. The boxes insulated the heat which could not dissipate and ignited.