The city activated its medical disaster plan as 29 people including 11 children needed to be evacuated.
Kortrijk mayor Vincent Van Quickenborne: "There was an awful lot of smoke and as a consequence the entire block of flats needed to be evacuated. But all in all this was a small fire that was soon under control."
"We think that this was probably arson. There are CCTV images so we will probably be able to identify the arsonist."