Firefighters were called to reports of a gas leak on Waterloo Road at the junction with The Cut in Waterloo.
An 18 inch gas main ruptured in the roadway. Around 400 office workers and 200 people from a theatre, were evacuated as a precaution and a cordon was set up.
A London Fire Brigade spokesperson said: "Although this is incident is now over for the Brigade, Waterloo Road remains closed from The Cut to Pearman Street.
"Motorists and pedestrians are asked to avoid the area."
The Brigade was called at 1421 and the incident was over by 2006. Three fire engines and around 15 firefighters from Dowgate, Lambeth and Euston fire stations were in attendance.