Dublin, May 22 (IANS): Polling stations in the Republic of Ireland opened their doors on Friday morning to some three million voters who will decide on the legalisation of same-sex marriage in a nation-wide referendum.

Citizens will have 15 hours to cast their ballots, and if a majority supports the measure, Ireland will be the first predominantly Catholic nation to allow gay and lesbian couples to get married as a result of popular will, Efe news agency reported.

The vote-count will begin on Saturday morning and first estimates could be out by noon, while the final result is expected to be announced a few hours later.

Projections have given a comfortable lead to same-sex advocates, although their opponents have gained ground in recent weeks, while a significant percentage of the electorate remain undecided.

On the ballot, the voters must select a simple “yes” or “no” to the proposition tendered by the Irish government coalition between Conservatives and Labour, which would defend the right that "marriage can be contracted according to the law for two people regardless of their sex".

In contrast, critics, including anti-abortion groups, ultra-conservatives and the Catholic Church, argue that these unions undermine the values of traditional family, and radically alter the processes of adoption and surrogacy, in addition to eroding the rights of the child.

The Republic of Ireland enacted the law on civil partnership in 2010, giving legal recognition to unmarried couples of the same sex for the first time in the country, but the law avoids describing unions as marriage, and they lack constitutional protections.

In another referendum also to be held on Friday, Irish voters will decide whether to cut the minimum age required to be president, which is a largely honorary post in the European country, from 35 to 21 years old.