Hitching an Irish flag to the baggage rack, the green-shirted fans take their seats in the express train to Poznan, where Ireland take on Croatia in their Euro 2012 opener on Sunday.

One adjusts his jester-style wig in the Emerald Isle's colours of green, white and orange, and cracks a joke - in fluent Polish.

Supporting two teams in a football tournament may be common among fairweather fans, but for Poles, the sentimental pull of Ireland means it's about far more than hedging their bets.

"We support Poland and we support Ireland too," 35-year-old Tomasz Nawrot told AFP.

"The Irish have great support from Poles. It seems like half of the Polish nation has relatives in Ireland!"

Ireland is home to tens of thousands of Poles, including Nawrot, who had travelled over specially for Euro 2012.

Ireland, along with Britain and Sweden, threw open its labour market to citizens of ex-communist states such as Poland as soon as they joined the European Union in 2004.

Estimates for the size of the Polish community in Ireland stretch from 150,000-250,000 - many of them having moved there during the property boom which opened the way for thousands of construction jobs - making them one of the biggest minority groups in the country of 4.5 million.

Even Ireland's economic woes, compared to Poland's growth, have not led huge numbers to go home, with many Polish migrants saying they prefer the more relaxed Irish lifestyle.

Nawrot and a group of friends - including one Irishman - had watched hosts Poland draw 1-1 in the tournament opener against Greece on Friday in the capital Warsaw.

After partying for two nights, they switched into their Ireland shirts and boarded the morning train for Poznan in the west of the country.

"We believe both teams are going to get to the quarter-finals," said Nawrot.

"Hopefully the Irish fighting spirit will see them through."

Irish supporters said they were touched by the Polish support.

"The Poles seems to be very fond of the Irish," said Derrick Murphy, standing in the train's packed corridor.

"We want to see Poland do well at Euro 2012, not just Ireland. It would be great for them, as they're the hosts," said his friend Frank Kerr.

"We like them because they're underdogs," added Murphy.