Centre-right party Fine Gael looks set to lead the next government - but without an overall majority, according to an exit poll in the General Election.
The party recorded 36.1% support - its highest result since November 1982 - according to the Millward Brown Lansdowne study commissioned by broadcaster RTE.
Labour, which hopes to be in coalition with Fine Gael, is on 20.5%, its best ever share of the vote.
Outgoing ruling party Fianna Fail is on a record low of 15.1%.
Sinn Fein's support is put at 10.1%, with outgoing coalition partners the Greens on 2.7% with the Independents and others polling 15.5%
The exit poll interviewed 3,500 voters after casting their ballots outside polling stations across 43 constituencies yesterday.
Official counting of the General Election votes will begin at 9am.
The same RTE exit poll in the last general election in 2007 was accurate to within 0.5% of the final result.
The first official results are due around mid-afternoon.
Voter turnout was reported to be one of the highest for many years with officials putting the figure in the region of 70%.
Almost 3.2 million voters were registered to cast their ballots, with more than 550 candidates running in 43 constituencies for 165 of the 166 seats.
Ceann Comhairle Seamus Kirk, the Dail speaker, is automatically returned.
The exit poll put support for Fine Gael lower than some opinion polls had suggested, where they had been tipped to secure as much as 40% of the popular vote, potentially allowing for a single-party government propped up by independents.
Taoiseach-in-waiting Enda Kenny, the Fine Gael leader, will be in his home town of Castlebar, Co Mayo today where his party is being tipped to take four of the five seats in the western constituency.
Mr Kenny should get a strong indication of the strength of his support by late tonight.
Fianna Fail leader Micheal Martin will be in Cork. Opinion polls throughout the campaign tipped the party for near electoral wipeout, recording support in the low teens.
The party has been in power for the last 14 years, overseeing some of the strongest years of the Celtic Tiger, but was also roundly blamed for the devastating recession of the last three years.
Despite Mr Martin's popularity after taking the helm of Fianna Fail from outgoing Taoiseach Brian Cowen, the party, which has been in power for 60 of the last 80 years, has seen its support base erode dramatically due to the impact of the downturn.
Fianna Fail's expected poor showing is a signal of the shift away from old divisions shaped in the early years of the State, known in Ireland as Civil War politics.
Labour is hoping to extend its support further afield than its traditionally strong urban bases.
The Green Party, a coalition government partner for the last four years, is battling to retain its popularity in Dublin with two former ministers in a fight for political survival.
They are also fighting for the last seats in Louth, Carlow-Kilkenny, Galway West and Cork South Central.
A record number of independents have also joined the race to drive change in Irish politics.
Fine Gael's deputy director of elections Frank Flannery said if the exit poll is accurate the election will mark a historic occasion.
"From my party's perspective we will be far and away the biggest party in the Dail for the first time ever," he said.
"It's a pretty disastrous poll from Fianna Fail's point of view."
He told RTE Radio Fianna Fail could have a "dramatically horrific election".
Fianna Fail's director of elections Tony Killeen said the polls signalled a massive volatility in the electorate never seen before.
"It is a worrying time and obviously for my own colleagues in Fianna Fail there will be excellent TDs and candidates who'll be beaten on this result," he said.
But he denied it could be the end of Fianna Fail as a movement.
The Fianna Fail support in Dublin was forecast to fall from 18 seats down to as low as one - Brian Lenihan appearing to be the only party candidate able to retain enough votes.
Noel Dempsey, a former Fianna Fail minister retiring from politics, said a nationwide total of 20-plus seats was all the party could hope for.
"It's looking pretty grim," he said.
"And to get a result in the low 20s would be good."