Eight fire engines and around 60 firefighters were called to a building fire on Battersea Park Road in Battersea.
The fire involved a three-storey building with commercial properties on the ground floor and flats above. Two flats on the second floor, along with part of the roof of the building, were damaged by fire. There were no reports of any injuries.
A London Fire Brigade spokesperson said: "Two occupants inside one of the flats were alerted to a smoke alarm sounding. They then found smoke coming from a bedroom and evacuated the building and called 999.
"This incident highlights just how important it is to have working smoke alarms fitted, on every level of your home. It allowed the occupants to escape unharmed whilst the fire was still relatively small.
“Smoke alarms give the earliest possible warning when a fire starts and we would urge everyone to make sure they have one fitted in every room where a fire can start except kitchens or bathrooms where heat alarms are more appropriate.”
People in the area were advised to keep their windows and doors closed at the height of the fire due to smoke travelling from the incident.
Battersea Park Road was closed between the junctions of Queenstown Road and Havelock Terrace, causing significant traffic disruption.Motorists were advised to avoid the area whilst firefighters remained on scene. The road has now reopened.
The Brigade received the first of 17 calls about the fire at 1428 and Control Officers mobilised crews from Clapham, Battersea, Lambeth, Brixton and surrounding fire stations to the scene. A 32-metre turntable ladder from Clapham Fire Station also attended and was used as a water tower to help extinguish the fire from above.
The fire was brought under control by 1555.
The fire is being treated as accidental and is believed to have been caused by a fault in a USB charging plug for an LED table lamp.