Ireland is voting in a referendum on a key European Union fiscal pact that is designed to strengthen the euro, in a vote that is seen as a verdict on EU and IMF-imposed austerity measures.
Opinion polls taken ahead of Thursday's vote indicated that the majority of Irish votes were likely to vote to back the accord.
Prime Minister Enda Kenny said on Wednesday that by ratifying the fiscal pact, which would punish countries that sign up if they fail to balance their budgets, Ireland would send a signal it will "never run riot with the people's money again".
"This is about stability, bringing confidence to the euro," the premier said as he campaigned at Dublin railway station.
Kenny said a 'yes' vote on the German-backed pact would show Europe that Ireland could lead by example.
"When we take over the EU presidency next year we want to be very effective," he told AFP. "A strong 'yes' vote adds to the respect and our credibility with our colleagues in Europe."
Voting was slow on Thursday as heavy rain appeared to discourage people from turning out. It was expected to pick up, however, before polling stations close at 10:00 pm local time (21:00 GMT).
A result is not expected until Friday.
'Austerity doesn't work'
Ireland was forced to seek an 85bn-euro ($106bn) bailout from the EU and IMF in 2010 after its property bubble burst and its banking sector was left on the brink of collapse.
The debt-laden government argues that only countries that ratify the fiscal pact can get guaranteed help from the European Stability Mechanism, the permanent bailout fund that comes into force in July and which it may well have to access.
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Four opinion polls at the weekend suggested that around 60 per cent of voters would back the treaty - but with a third still undecided, there is still a possibility Ireland could deliver a shock "no" vote, as it has done in two previous EU referendums.
Critics of the pact have been quick to tap into public anger against the tax rises and spending cuts brought in after the bailout, branding it an "austerity treaty" as it ultimately empowers the EU to fine countries that overspend.
"We know that austerity doesn't work, and that's increasingly what people are saying in mainland Europe," Gerry Adams, leader of the Sinn Fein, the main party opposing the pact, said outside the Irish parliament.
"It is not a good thing for us to hand over fiscal authority to unaccountable bureaucrats."
Constantin Gurdgiev, a Dublin-based economist, told Al Jazeera that a 'no' vote would be surprising, but would have significant implications.
"The 'no' vote would throw a significant surprise both into the European equation, and also into the Irish policy-makers situation as well. First of all the 'no' vote will mean a huge uncertainty, or a very significant uncertainty about the future funding for the Irish state, especially once the current bailout package runs out in 2013," he said.
"However, at the same time, [Irish voters] are very aware right now that the entire equation, the entire crisis is now moving on. It has now swept across Spain and now the entire European Stabilisation Mechanism is under threat."
A "no" vote in Thursday's referendum would not halt the fiscal pact - which all 27 EU members except Britain and the Czech Republic have signed - as it will come into force after just 12 countries have ratified it.