The eastern end of Southwark Street was closed to traffic and pedestrians on Sunday after a 34-year-old man was assaulted in the early hours of the morning.
Police were called to Southwark Street at 4.50am to reports of an assault.
A 34-year-old man was taken to hospital where he is in a serious but stable condition.
One person has been arrested in connection with the incident.
Southwark Street was still closed at midday on Sunday and buses that normally run southbound along Borough High Street were diverted via Tooley Street and Tower Bridge Road.
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