The Brigade was first called at 12.12am and crews brought the situation under control by 1.36am this morning (December 18).
Around 50 residents left the building before four fire engines and 25 firefighters arrived on scene.
A 25m cordon was set as crews made sure the building was safe.
Part of a utilities cupboard on the ground floor was damaged in the fire.
Firefighters from Tooting, Wimbledon, Mitcham and nearby stations attended.
No injuries were reported during the incident.
The cause of the fire remains under investigation by the Brigade and Metropolitan Police Service.
A spokesperson for London Fire Brigade: “Four fire engines and around 25 firefighters tackled a fire at a block of flats on Tooting High Street on Monday.
“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.”