Firefighters responded to reports of a gas leak on New Bridge Street in Blackfriars.
A 100m cordon was put in place and around 400 people were evacuated from surrounding buildings as a precaution while crews worked with partners to isolate a 24-inch gas main and make the scene safe. There were no reports of any injuries.
There were road closures in place, which were causing some disruption, and the public were encouraged to avoid the area where possible.
The Brigade was called at 1059 and firefighters began to leave the scene at 1808. Four fire engines and around 25 firefighters from Dowgate, Soho, Kentish Town and Clapham fire stations attended the scene.