Voter turnout in part Dublin and parts of Leinster looks to have exceeded that of the same-sex marriage referendum three years ago.
The turnout in Wicklow alone was at 70% about an hour before the polls closed.
This compared with a total turnout for that county of 68% for the last referendum.
It was a similar story in many parts of Dublin, where turnout was estimated at over 65% in many places.
Across the country more than 50% have voted in most areas, with one area in Limerick reporting 80% turnout.
These figures suggest the turnout could be on par with the 61% figure recorded for the same-sex marriage referendum three years ago.
Whatever the final figure this will be one of the highest turnouts for a referendum.
The ballot boxes will be opened at 9am and the first results are expected before lunchtime.
Our correspondents have the latest on referendum turnout figures around the country pic.twitter.com/oNqqzsoGVw
— RTÉ News (@rtenews) May 25, 2018
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