Police launched an investigation after the fire started around 9.40am today (July 7) in Electric Avenue.
The blaze was under control around three-and-a-half hours later.
People were evacuated, with Brixton Underground station, the Victoria line and roads closed.
Police confirmed a man in his 40s has been arrested on suspicion of arson and remain in police custody.
A crime scene has been established and emergency services remain at the scene.
Anyone with information about the incident is asked to call police on 101 quoting CAD 2087/07JUL or to remain anonymous call Crimestoppers on 0800 555 111.
