Images and videos of the incident showed dozens of youths tearing down fences, throwing beer bottles and fireworks at police, and chanting slogans against the proposed centre for asylum-seekers.
According to national broadcaster NOS, around 2,000 people joined the protest in a town of 27,000.
A meeting of the town’s council to decide on whether to build the centre to house 1,500 asylum-seekers had to be halted. A regional broadcaster showed footage of the meeting being evacuated by shouting policemen as rioters sought to force their way into the building.