Five people were arrested, more than 20 detained and eight policemen injured late on Tuesday when a group of about 350 people attempted to force their way into an abandoned factory in Patra, where dozens of undocumented migrants are squatting.
Police said the crowd that had gathered outside the Peiraiki Patraiki factory consisted of Patra residents who were protesting the fatal stabbing of a local man and supporters of the neo-Nazi Chrysi Avgi.
They clashed with police, who used tear gas to repel the crowd, and set fires outside the factory. Police said that they suffered repeated attacks and were on the receiving end of rocks, flares and other missiles.
Tension in the area has risen following the murder of a 30-year-old local man. Three Afghans are suspected of carrying out the attack in an area next to the port, where hundreds of migrants gather in the hope of making it onto a ferry to Italy.
Police also reported an attack on Tuesday night on a journalist and a Chrysi Avgi MP after the pair had held a discussion on a local TV station.
Officers said that several people attacked the deputy, Michalis Arvanitis, and then set upon the journalist, Apostolos Vouldis, when he tried to deter them.