Irish voters had their say over the European Union's Lisbon treaty in a referendum on Thursday, the only citizens in the 27-member bloc to be entrusted with a vote on the replacement for a rejected EU constitution.
The treaty, intended to make the EU stronger and more effective, has the backing of all the main political parties in a country that has prospered from its membership of the bloc.
Bookmakers say the odds are heavily in favour of a "Yes" vote but an opinion poll last week had put opponents of the treaty briefly ahead, alarming EU leaders.
The entire project could be doomed if Irish voters reject it and no alternative plan has been prepared. The outcome will not be known until Friday.
Public broadcaster RTE said turnout appeared light, hovering close to 20 percent in most areas by late afternoon although polls do not close until 10 p.m. Light turnout could help the "No" camp whose backers have strongly held views.
"I genuinely think a lot of people will not make up their mind until they stand in the ballot box with a pen in their hand," said Damian Loscher, head of pollsters TNS mrbi.
The last opinion poll of the campaign, published at the weekend, showed the "Yes" vote narrowly ahead.
The approval of all member states is required to ratify the treaty which replaces a constitution abandoned after it was rejected by French and Dutch voters in 2005.
This time all other EU countries have avoided holding popular votes. Ireland's constitution requires a referendum on any amendments, giving make-or-break power to voters in a nation with less than 1 percent of the EU's 490 million population.
The treaty envisages a long-term president of the European Council of EU leaders, a stronger foreign policy chief and a mutual defence pact. It would also develop a more democratic voting system and give a greater say to Europe's parliaments.
Finance Minister Brian Lenihan told Reuters canvassing by his party indicated the "Yes" camp had regained momentum and said the EU had no fallback position if the pact is rejected.
