A historic vote is taking place in Ireland Friday as the republic becomes the first nation in the world to hold a referendum on legalising same sex marriage.

Polling stations opened at 7 a.m. local time and will remain open until 10 p.m. with a count scheduled for Saturday (May 23).

Some three million voters have been invited to cast ballots across Ireland’s 43 constituencies, the Guardian reports.

They'll be asked whether they agree with the following statement: "Marriage may be contracted in accordance with law by two persons without distinction as to their sex."

Same-sex marriage is currently legal in 19 countries worldwide, but this is the first time a public referendum has been held. Only registered Irish citizens who are living in the state can take part.

Carmelite sisters leave a polling station in Malahide, County Dublin, Ireland, Friday, May 22, 2015. Image: Peter Morrison/Associated Press

The issue has been the subject of fierce debate, but the country is widely expected to vote yes. However, government officials and gay rights activists are advising caution given Ireland's track record in producing surprise referendum results, the Associated Press reports. They say achieving a high voter turnout is crucial, particularly among younger citizens who traditionally don't vote in great numbers.

In recent days, a series of murals across the country have advocated legalisation and a slew of comedians including Stephen Fry and Trevor Noah have voiced their support for the yes vote.

Numerous companies, from eBay to Twitter and Ben & Jerry's have signed up to Business For Yes Equality and Hailo unleashed a series of rainbow coloured cars in Dublin to show their support. Google also threw their hat in the ring.

Google Ireland is sporting some good politics today google.ie pic.twitter.com/QpSD5s7jOg — Dr. Corbett Moran (@corbett) May 21, 2015

Ireland's prime minister, Enda Kenny, urged voters to support marriage equality ahead of the vote.

For gay sons&daughters, brothers&sisters, family&friends, Yeats said it best "Tread softly because you tread on my dreams." #MarRef — Enda Kenny (@EndaKennyTD) May 21, 2015

Both of the ruling coalition parties, Fine Gael and Labour, echoed his sentiments.

A group of evangelical Catholics and Protestants, meanwhile, have reportedly distributed over 90,000 anti-gay marriage leaflets over the last week.

The first female Anglican bishop in Ireland, Pat Storey, also wrote to her clergy explaining her reasons for voting no.

The result is expected at some point on Saturday afternoon.