Police detained three people for resisting arrest and other minor crimes during a street vigil in downtown Tampere Thursday evening.
The street occupation spiraled out of control into violence in when police attempted to break up the demonstration.
The protest began around 5.30 pm, and involved some 200 demonstrators calling for more recreational space, non-commercial culture and fewer motorists.
Around ten o'clock last night, officers attempted to disperse the crowd that had gathered on Satakunta Street, in accordance with public order regulations.
However scores of them refused to leave, and began throwing bottles and beer cans at the police. One officer was injured when he was struck on the head.
Police were forced to use gas to control the mêlée but were finally able to bring the situation under control later in the evening.
Officials say they will unravel the evenings events with the help of surveillance cameras.