Police arrested 34 people, mostly Britons, early on Wednesday after a second night of violence in Portugal's Algarve tourist region.
Hooligans wearing England soccer shirts threw bottles and chairs at police in the same area in the resort town Albufeira, where about 200 fans rioted the previous night.
Police armed with batons moved in to disperse the crowd.
"I can say that there are 34 arrested," a spokeswoman for the GNR paramilitary force said. Those detained included 33 Britons, a British embassy spokesman said.
Tens of thousands of fans are in Portugal for the 16-team European Championship, which ends on July 4.
England fans have a reputation for hooliganism and caused serious trouble in France during the 1998 World Cup finals and in Belgium at the last European Championship in 2000.
Later on Wednesday 12 Britons, a Russian and a Portuguese appeared in court accused of causing a public disturbance.
GNR captain Manuel Jorge said up to 400 people were involved in the clashes on Wednesday morning. Two Britons and one police officer were slightly injured, Lusa news agency said.
European soccer's governing body UEFA and Britain's Home Office (interior ministry) said the violence in Albufeira had little to do with the England team and a lot to do with druken young men on holiday.
UEFA had warned the English Football Association that the national team could be banned from the tournament if fans cause trouble in Portugal.
The head of the British police force offering advice at Euro 2004 said the rioters were a disgrace but added that the incidents bore no signs of organized soccer hooliganism.
Prime Minister Tony Blair said they brought shame on their country.
"In respect of the outbreaks of disorder let me make it make it absolutely clear those are completely intolerable and the police should come down very heavily and will do, I have no doubt at all," he told parliament in London.
William Gaillard, UEFA's communications director, said: "The UEFA position is as it was the night before. This is unrelated to football and the sort of thing that happens in the Mediterranean in the summer."
England play Switzerland in Coimbra, north of Lisbon, on Thursday in their second game at the three-week tournament.