A full recount has been announced in the Ireland South constituency for the European Parliament, which the constituency's returning officer has said may cost up to €1 million, and could take up to 28 working days.

The move follows a recheck of the vote of Sinn Féin's Liadh Ní Riada and the Green Party's Grace O'Sullivan.

The recheck resulted in Ms Ní Riada picking up just one vote from almost 200,000 papers.

Making the recount announcement in Cork, returning officer Martin Harvey said: "Having completed the recheck of Liadh Ní Riada and Grace O'Sullivan's papers, Liadh Ní Riada has confirmed that she wishes to proceed with a full recount of all the papers.

"Accordingly the count is now adjourned and will resume here at 9am on Tuesday next the 4th of June.

The full recount could take up to 28 working days, or six weeks.

Mr Harvey said the recount may cost up to €1m, but the true cost has not been estimated yet.

He also said it will be difficult to get the necessary staff to carry out the recount, but it will be done and will take time.

Ms O'Sullivan's election agent, Ed Davitt, said that he understands the basis for the recount but he is disappointed.

He said that given the outcome of the recheck, a full recount is unlikely to give a different result.

Mr Davitt said it has serious implications for the makeup of the new European Parliament and Commission given the recount is unlikely to be concluded before mid-July.

Sinn Féin's Director of Elections Jonathan O'Brien defended the decision to call for the recount saying that in essence only 2% of all the 750,000 votes cast were checked.

"Will it make a material difference? The only way we will know is to have a full recount," he said.

Asked about the cost, he said he would not put a price on democracy.

Read more: Elections 2019

Fine Gael's Seán Kelly had taken the first seat in the constituency.

He was followed by Fianna Fáil’s Billy Kelleher, who exceeded the quota on the 17th count.

Independents 4 Change candidate Mick Wallace is virtually guaranteed a seat, with just over 109,000 votes after the 17th count.

Ms Ní Riada is in a tight battle with Ms O'Sullivan and Fine Gael's Deirdre Clune for the final two seats, with one of the three set to miss out.

Meanwhile, re-elected Sinn Féin MEP Matt Carthy has said the party's disappointing showing in the European and local elections means there are big questions for the party to answer.

The Midlands-North-West MEP added it is clear that people who previously voted for Sinn Féin either did not vote for the party this time or did not bother to turn out to vote.

Mr Carthy said there appeared to be a number of peculiar issues behind the trend.

He said that some issues were localised but there are also a number of macro issues that need to be addressed.

The media has, he said, magnified a number of localised disputes which may have caused some problems.

In addition, he said, many people are frustrated by the failure of the Northern Institutions to be re-established.