Four fire engines and 21 firefighters and officers were called to a fire at a flat in Manciple Street, Borough, last night.
Part of a fifth-floor maisonette was damaged by fire.
Watch Manager Mick Corcoran, who was at the scene, said: "Smoke alarms fitted in the flat went off and alerted neighbours, who raised the alarm.
"The resident did the right thing in getting out quickly when he saw smoke..
“Homes need multiple smoke alarms or you won’t be properly covered. Ideal spots for smoke alarms include rooms where you leave electrical equipment running like satellite boxes, computers or heaters; any room where you smoke, and anywhere you charge your mobile or laptop.
“As a minimum you should have smoke alarms on every floor - in the hallways and the rooms you use the most, plus a heat alarm in the kitchen. They should be tested regularly."
The Brigade was called at 2045 and the fire was under control at 2130. Fire crews from Dockhead, Dowgate, Old Kent Road, and Lambeth River fire stations attended the scene.
The cause of the fire is under investigation.