Prime Minister Leo Varadkar on Saturday hailed Ireland's "quiet revolution" after exit polls and early results showed Irish voters had overwhelmingly supported repealing a decades-old ban on abortion in the mainly Catholic country.
Results from the first four of 40 constituencies to declare showed 66.36 per cent voted "yes" and 33.64 per cent voted "no", on a 62 per cent turnout.
The "yes" vote was at 77 per cent in Dublin Central, 69 per cent in Cork South-Central, 64 per cent in Cork North-Central and 60 per cent in Galway East.
The results bear out exit polls conducted after Friday's vote on repealing a 1983 constitutional amendment that led to some of Europe's strictest abortion laws.
A poll of 4,000 voters for The Irish Times newspaper put the pro-choice camp ahead by 68 per cent to 32 per cent, while a second survey of 3,800 voters by national broadcaster RTE put the margin at 69 per cent to 31 per cent.
"What we've seen today is the culmination of a quiet revolution that has been taking place in Ireland for the past 10 or 20 years," Mr Varadkar told RTE.
"The people have said that we want a modern constitution for a modern country, that we trust women and that we respect them to make the right decisions and the right choices about their own health care."
Mr Varadkar said he planned for a new law to allow abortions to be in place by the end of the year. Health Minister Simon Harris said the cabinet would meet on Tuesday to approve the drafting of legislation.
The government has proposed that if the amendment is repealed, abortion will be allowed in the first 12 weeks of pregnancy and between 12 and 24 weeks in exceptional circumstances.
The referendum 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 per cent.
Mr Varadkar, Ireland's first gay prime minister, came to power last year in what was seen as another major milestone for diversity in Ireland.
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 per cent in favour of the proposal and men by 65 per cent.
People over 65 voted 60 per cent against repealing the current legislation, which only allows terminations in cases where the mother's life is in danger.
However, all other age groups backed the proposal, with support at 87 per cent among the youngest voters, aged 18 to 24.
Around 3.5 million people were eligible to vote in the referendum, with the final result to be declared at Dublin Castle.
Even before the first constituency was declared, the official Together for Yes campaign to repeal the abortion ban said they had passed more than a million votes, and were running at 68 per cent support.
In Dublin, many voters welcomed the expected overwhelming result.
Catherine Claffey, 53, a flower seller on the capital's main Grafton Street shopping thoroughfare, said: "We've pulled ourselves out of the dark ages. We're not a backward country any more, the way the church would have had us thinking."
John Kelly, 62, said: "I'm actually very proud of it."
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.
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.
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Ireland's eighth amendment recognises the "right to life of the unborn" with an "equal right to life of the mother".
The amendment was introduced after a 1983 referendum that approved a constitutional ban on abortion.
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.
Art director Aoife Murray, 27, who voted in Dublin, said the exit poll left her in tears of relief.
"It's mad that there would have been people flying in to vote and a number of women in that airport waiting to leave to go and have an abortion," she said.
Naomi Long, leader of the Alliance Party in neighbouring Northern Ireland, said "eyes will now turn" north of the border, where abortion and same-sex marriage remain illegal, unlike the rest of the United Kingdom.