Six fire engines and around 40 firefighters were called to an office block under refurbishment into flats on Blagdon Road in New Malden.
Part of a flat on the seventh floor was damaged by fire. Firefighters prevented the fire from spreading further.
The fire was noticed by a passer-by who called 999.
The Brigade was called at 2140 and the fire was under control by 2331. Fire crews from New Malden, Surbiton, Wimbledon, Kingston and Sutton fire stations attended the scene. The cause of the fire is under investigation.