A fire that roared through a three-story building in Adelaide and brought parts of the CBD to a halt was deliberately lit, police say.

SA Police said today they wanted to speak with a man on a mountain bike who was captured on CCTV cameras leaving the scene. The man was a “person of interest”, not a suspect.

The fire took half the city’s firefighters to contain and destroyed the Wing Chun Martial Arts Academy.

Police believe last Tuesday’s blaze started behind the building on Hindley Street.

– with AAP