Latest figures from the Irish Times reveal that the 'no' campaign has already claimed a victory in a number of constituencies, including Mayo and Galway West. Early counts also show Dublin is split 60-40% against the Treaty.
Analysts had warned that the EU's new Lisbon Treaty would have more chance of being rejected if the turnout was poor, because anti-EU voters tend to be much more motivated to go to the polls.
And despite heavy government lobbying, it appears that less than half of the Irish electorate went to the polls yesterday (12 June) to give their verdict.
"It's knife-edge stuff," a government party source told Reuters, acknowledging that the authorities had counted on a higher turnout.
Low turnout was also a crucial factor in the defeat during Ireland's last European referendum in 2001, when just 35% of the Irish citizens shot down the Nice Treaty. Nevertheless it was passed in a second vote with turnout at 49%.
As the treaty needs the approval of all 27 member states to come into force, in effect, this means that less than 1.3 million people decided the future of Europe's 495 million citizens.
An Irish 'no' would throw the EU into a deep crisis, as EU leaders have repeatedly said there is no 'Plan B' in case of an Irish 'no' vote.
French Prime Minister François Fillon spoke more frankly in an interview on French television yesterday (12 June), saying an Irish rejection of the Lisbon treaty would mean the end of an accord for the European constitution. But France's Europe Minister Jean-Pierre Jouyet said ratification should continue even if Ireland votes 'no'.
Meanwhile, the UK government signalled that it would nevertheless continue the parliamentary ratification process even if Irish voters rejected the treaty.
"Our intention is to go ahead with this as planned," a British diplomatic source told AFP.
The upper House of Lords will next week consider the treaty, which has already been approved by the lower House of Commons.
EurActiv will keep you updated with the results of Ireland's referendum as they become known. Full results are due at 15.00 (16.00 CET).
