London Bridge was closed and buses were diverted away from a 12-storey building when fire broke out behind scaffolding.
London Fire Brigade (LFB) sent four fire engines to the blaze on King William Street shortly after 18:00 GMT.
Photographs on social media showed flames behind the scaffolding but by 21:00 the fire was under control.
At the scene, BBC reporter Alan Soady said: "The building is covered in scaffolding with white netting. You can see that there are flames behind it."
There were no reports of injuries but the bridge was cordoned off.
"They'd have been worried about any burning debris falling down on to the path and the road that's so busy during rush hour," he said.