Four fire engines and around 25 firefighters tackled a fire at a block of flats on Tooting High Street.
Part of a utilities cupboard on the ground floor was damaged by the fire. Around 50 people left the building before the Brigade arrived. There were no reports of any injuries.
A 25-metre cordon was in place as a precaution whilst crews worked to make the scene safe.
The Brigade was called at 0012 and the fire was under control by 0136. Firefighters from Tooting, Wimbledon, Mitcham and surrounding fire stations attended the scene.
The cause of the fire is under investigation by the Brigade and the Metropolitan Police Service.