Firefighters were called to a gas leak on Bowyer Street in Camberwell.
A gas main on the exterior side of a residential block ruptured. Around 100 people were evacuated as a precaution and a safety cordon was in place. There were no reports of any injuries.
Crews carried out a sweep of the building to check increased levels of chemical substances were no longer present.
The Brigade was called at 2058 and the incident was over for firefighters by 2326. Two fire engines and two fire rescue units from Peckham, Brixton, Lewisham and Bethnal Green fire stations are at the scene.