Three fire engines and around 15 firefighters were called to a burst water main at the junction of Blackfriars Road and Union Street in Southwark.
An area of approximately 7,500sqm was flooded to varying depths and around 30 nearby properties were also affected.
Crews worked to pump water away from the affected properties and firefighters assisted one woman from a lower ground floor flat. There were no reports of any injuries.
Borough Commander Richard Tapp, who was at the scene, said: "The burst water main caused significant flooding in a very busy area.
"Southwark tube station was closed and there were also several local road closures in place which had an impact on traffic.
"Some road closures remain in place and drivers are advised to avoid the area if possible."
The Brigade was called at 0509 and the incident was over for firefighters by 1007. Fire crews from Dowgate and Lambeth fire stations were at the scene along with Thames Water and the Metropolitan Police Service.