Figures suggest the Republic of Ireland has voted to legalise same-sex marriage in a historic referendum.
More than 3.2m people were asked whether they wanted to amend the country's constitution to allow gay and lesbian couples to marry.
Government ministers have said they believe it will pass, while prominent "no" campaigners have conceded defeat.
Counting started at 09:00 BST on Saturday morning. An "unusually high" turnout has been reported.
A final result is expected late afternoon on Saturday.
If the change is approved, the Republic of Ireland would become the first country to legalise same-sex marriage through a popular vote.
Minister for Health Leo Varadkar, who earlier this year came out as the Republic of Ireland's first openly gay minister, said the campaign had been "almost like a social revolution".
What 'yes' vote would mean
The Republic of Ireland has a written constitution which can only be changed by referendum.
If the proposal is passed, a marriage between two people of the same sex would have the same status under the Irish constitution as a marriage between a man and a woman.
They would be recognised as a family and be entitled to the constitutional protection for families.
Civil partnerships for same-sex couples have been legal in Ireland since 2010, giving couples legal protection which could be changed by the government.
However, if the vote is passed, married gay people would have a constitutional standing that could only be removed by another popular vote.
Speaking from the Dublin count, he told Irish broadcaster RTE that it appeared about 75% of votes being counted there were in favour of legalising same-sex marriage.
Some prominent "no" campaigners have conceded defeat.
David Quinn of the Iona Institute, a Catholic group, said it was "obviously a very impressive victory for the 'yes' side".
"Obviously there's a certain amount of disappointment, but I'm philosophical about the outcome," he told RTE.
"It was always going to be an uphill battle - there were far fewer organisations on the 'no' side, while all the major political parties were lined up on the 'yes' side and you had major corporations coming out for the first time to say how we should vote on a particular issue."
The upper courtyard of Dublin Castle is open to 2,000 people for people to view the declarations on a large screen.
Before Friday, votes had already been cast in some islands as well as hospitals, hospices and nursing homes. Irish citizens who are registered were allowed to vote, but there was no postal voting. Many people returned to Ireland to cast their votes.
They were asked whether they agreed with the statement: "Marriage may be contracted in accordance with law by two persons without distinction as to their sex."
The referendum was being held 22 years after homosexual acts were decriminalised in Ireland.
In 2010, the Irish government enacted civil partnership legislation, which provided legal recognition for gay couples.
But there are some important differences between civil partnership and marriage, the critical one being that marriage is protected in the constitution while civil partnership is not.
A constitutional convention established by the Irish government in 2013 considered the specifics of a proposal on extending marriage rights, as well as discussing other changes to the constitution.
It voted in favour of holding a referendum on same-sex marriage and the date was announced by Taoiseach (Prime Minister) Enda Kenny earlier this year.
If the measure is passed, Catholic churches will continue to decide for themselves whether to solemnise a marriage.
The leader of the Catholic Church in Ireland, Eamon Martin, has said the church may look at whether it continues to perform the civil side of solemnisation if the change comes in.
A separate referendum, on whether the eligibility age of presidential candidates should be lowered from 35 to 21, was being held at the same time, along with a parliamentary by-election in the Carlow-Kilkenny constituency.
Same-sex marriage is currently legal in 19 countries worldwide.