Tallies in the Dublin Central constituency suggest that the Social Democrats' Daniel Ennis is slightly ahead of Sinn Féin's Janice Boylan.
Tallies are unofficial figures compiled by observers at count centres. A first count is not expected until this afternoon.
With 100% of the boxes tallied, Mr Ennis is at 20%, Ms Boylan is at 18% and Independent Gerard Hutch, Fine Gael's Ray McAdam and the Green Party's Janet Horner are all on 11%.
Only around 500 votes appear to separate Mr Ennis and Ms Boylan.
A number of experienced tally people are calling the seat for Mr Ennis based on the transfer patterns they have observed in this tally and on the basis of the last general election.
Social Democrats TD for the constituency Garry Gannon said that party is "obviously delighted" with the tally.
"It is a real endorsement of the type of politics Social Democrats stand for and Daniel too," he said.
Yesterday's estimated turnout was 39% in this constituency, compared to 52% in 2024, with a high of 52% in Drumcondra and a low of 25% in the north inner city.
The bye-election was caused by Fine Gael's Paschal Donohoe leaving politics for a senior role in World Bank in the US.
Follow live updates on the Galway West and Dublin Central bye-elections
The full list of candidates is:
Janice Boylan (Sinn Féin)
Tony Corrigan (Independent)
Daniel Ennis (Social Democrats)
Colm Joseph Flood (Independent)
Mannix Flynn (Independent)
Janet Horner (Green Party)
Gerard Hutch (Independent)
Ray McAdam (Fine Gael)
Eoghan Ó Ceannabháin (People Before Profit)
Ruth O'Dea (The Labour Party)
John O'Leary (Independent)
Ian Noel Smyth (Aontú)
Malachy Steenson (Independent)
John Stephens (Fianna Fáil)
Additional reporting: PA
