Ireland looks set to "make history" by liberalising some of the strictest abortion laws in Europe, Prime Minister Leo Varadkar said as votes in the hard-fought referendum were counted Saturday.
The proposal to repeal the constitutional ban on terminations was predicted to win by a more than two-thirds majority, according to both exit polls.
A survey of 4,000 voters for The Irish Times newspaper put the pro-choice camp ahead by 68 percent to 32 percent, while a second exit poll of 3,800 voters by national broadcaster RTE put the margin at 69 percent to 31 percent.
"Democracy in action. It's looking like we will make history," Varadkar wrote on Twitter following a divisive and often emotional campaign.
The result looks set to be another hammer blow to the Roman Catholic Church's authority in Ireland, coming three years after referendum voters backed legalising same-sex marriage by 62 percent.
In what was traditionally one of the most religious countries in Europe, the Church's influence has waned in recent years following a series of child sex abuse scandals.
The referendum comes three months before a visit by Pope Francis for the World Meeting of Families.
The Irish Times survey suggested women voted by 70 percent in favour of the proposal and men by 65 percent.
People over 65, however, voted 60 percent against overhauling the current legislation, which only allows terminations in cases where the mother's life is in danger.
All other age groups backed the proposal, with support at 87 percent among the youngest voters, aged 18 to 24.
Urban voters were 71 percent in favour and rural voters -- thought to be the most conservative -- gave a predicted 60 percent support.
Figures from different constituencies are expected from 1100 GMT, with a final result to be announced later in the day at the main counting centre in Dublin Castle.
Varadkar's government has proposed that if the amendment is repealed, abortion will be allowed in the first 12 weeks of pregnancy and between 12 and 24 weeks in exceptional circumstances.
He has promised that a draft law will be published before the end of the summer with the aim of approval by the year's end.
Varadkar and Micheal Martin, leader of Ireland's other main party Fianna Fail, both support the legislation, meaning that it is widely expected to be approved.
The exit poll showed "an overwhelming desire for change that nobody has foreseen", wrote The Irish Times's deputy political editor Fiach Kelly.
"The victory for the 'Yes' campaign looks set to be neither narrow nor based on a few segments of Irish society. Rather, it will be carried high on the shoulders of a majority across the entire country," he said.
He called it "the final casting off of old mores".
Nearly 3.5 million voters were asked whether they wanted to overturn the ban.
Deputy Prime Minister Simon Coveney said the referendum had made him "proud to be Irish", forecasting "a stunning result that will bring about a fundamental change for the better".
The anti-abortion campaign, which wanted to keep the Irish constitution's eighth amendment, seemed prepared to accept a heavy defeat but vowed to stand firm.
"Abortion on demand would deal Ireland a tragic blow but the pro-life movement will rise to any challenge it faces," said prominent anti-abortion campaigner Cora Sherlock.
Save the 8th campaign spokesman John McGuirk said an unborn child's right to life existed "independent of what a majority says.
"That said, with a result of that magnitude, clearly there was very little to be done."
Abortion is still banned in some 20 countries worldwide, while others have highly restrictive laws in place. In the European Union, predominantly Catholic Malta is the only country with a total ban.
Ireland's eighth amendment recognises the "right to life of the unborn" with an "equal right to life of the mother".
Anyone terminating a pregnancy in Ireland currently faces up to 14 years in jail.
The law was tweaked in 2013 to allow terminations if the mother's life is at risk.
The ban has led to thousands of women travelling each year to neighbouring Britain, where terminations are legal, or increasingly turning to abortion pills sold online.
Since 1983, around 170,000 Irish women have gone abroad for terminations.
Naomi Long, leader of the Alliance Party in neighbouring Northern Ireland, said "eyes will now turn" to the British-ruled province, where abortion and same-sex marriage remain illegal, unlike the rest of the United Kingdom.