Four fire engines attended a chemical incident at Sampson House in Hopton Street on Sunday afternoon.
Six carbon dioxide fire extinguishers were accidentally set off in the basement of the IBM office building and data centre.
The London Fire Brigade says that around 15 people were evacuated from the offices as a precaution.
Firefighters wearing breathing apparatus inspected the affected area and made it safe by ventilating the premises.
The fire brigade was called at 12.51pm and the incident was over just after 3.30pm.
Crews from Southwark, Lambeth, Dowgate and Whitechapel stations attended the incident.
As well as the four fire engines a number of other fire brigade vehicles – including the scientific support unit – were sent to the scene.
As Hopton Street is currently part of the diversionary route for the Thames Path a heavy flow of pedestrians witnessed the scenes in the Bankside street.
Sampson House is part of the property portfolio formerly owned by Simon Halabi's companies. The block is currently being marketed for sale by the receiver.