More than 20 firefighters and five fire engines have been called to a fire at 25-storey Sudbury House in Wandsworth High Street.
Construction workers apparently saw smoke coming out a sixth floor letter box and called the emergency services.
The fire was quickly put out by crews from Clapham, Wandworth and Tooting and no was seriously hurt.
Sudbury House is situated behind the Soutside shopping centre in the High Street.
A spokesman for the London Fire Brigade said: "We were called at 11.24am to reports of a fire in the sixth floor of a 25-storey building, it was under control by 11.59.
"No damage to the property or injuries have been reported."
In August 2010 a panic-stricken man was preparing to jump from his fifth-floor flat in Sudbury House after a fire broke out there, but he was rescued by firefighters.
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