Six fire engines and around 40 firefighters were called to a fire on Stanstead Road in Lewisham.
Firefighters tackled a fire in a three-storey block of flats, where part of the roof of a flat on the third floor was destroyed by the fire. There were no injuries reported.
There will continue to be some traffic disruption on the South Circular between Elsinmore Road and the B128 Junction until all the fire crews have left the scene.
The Brigade was called at 0852 and the fire was under control by 1010. Fire crews from Forest Hill, Lewisham, Greenwich and other surrounding fire stations attended the scene.
The cause of the fire will be investigated.