Early results are expected later on Friday in an election that could potentially bring the province under London's direct rule unless the likely two main parties can break the deadlock.
The election was called in January when the Sinn Fein party -- once the political arm of the Irish Republican Army -- brought down the province's semi-autonomous government in protest at the Democratic Unionist Party (DUP), the pro-British party with which it shares power.
That triggered fresh elections to the Northern Ireland Assembly, a legislature in Belfast in which representatives of once warring communities have shared power on and off since a 1998 peace deal.
The conservative DUP won slightly more seats than the socialist and pro-Irish republican Sinn Fein in last year's election, giving them the right to chose their leader Arlene Foster as the province's first minister.
A similar result is forecast this time around, but Sinn Feinn have said they will not work with the DUP if Foster is re-nominated.
Final results are not expected until Saturday at the earliest.
If the two parties cannot resolve their differences within three weeks of the vote, the assembly's executive could be suspended and the province fully governed from London.
"We're up for going back into government but only on the basis of equality, respect and integrity," new Sinn Fein leader Michelle O'Neill told AFP.
"We cannot go into government with Arlene Foster as First or Deputy First Minister while there is a shadow hanging over her, but that doesn't mean we can't find a way forward."
Martin McGuinness, a former IRA commander who became the deputy first minister of Northern Ireland, resigned in January in protest over a botched green energy subsidy scheme rolled out by Foster when she was economy minister.
McGuinness is not standing again due to ill health, paving the way for O'Neill to take over.
jpegMpeg4-1280x720Foster has called on unionists to stand behind her pending an investigation into the energy scheme.
"If you feed a crocodile it will keep coming back for more," she told a party rally.
Old sectarian wounds were also reopened in Britain's vote in June to leave the European Union, which the DUP supported but Sinn Fein opposed.
Britain has signalled its intention to leave the EU's customs union after Brexit, raising fears of a new hard border between Northern Ireland and the Republic of Ireland, which will remain in the EU.
The possibility of a return to checkpoints has stirred memories of The Troubles, three decades of strife over British control of Northern Ireland, in which more than 3,500 people were killed.
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