The electorate is returning to the polls to select a new devolved Assembly for the second time in less than a year.
The powersharing coalition executive led by the two largest parties at Stormont - the Democratic Unionists and Sinn Fein - collapsed in January.
If the former partners in government are again returned as the main players, they will have three weeks to resolve their multiple differences and form a new administration.
The re-imposition of direct rule from London is on the cards if the post-election talks fail to mend tensions.
DUP leader Arlene Foster voted at Brookeborough primary school in the heart of her Fermanagh and South Tyrone constituency.
The former first minister chatted with local people outside and said hello to the gathered media.
Forty miles away, Sinn Fein’s northern leader Michelle O’Neill filled out her ballot paper in St Patrick’s primary school in her home village of Clonoe, Co Tyrone.
She was joined by daughter Saoirse and son Ryan. He has just turned 18 and was voting for the first time.
“It’s great that so many people are coming out to vote,” said Mrs O’Neill.
The Ulster Unionists and nationalist Social Democratic and Labour Party (SDLP), which have presented themselves as an alternative cross-community partnership, are bidding to wrest control away from the fractious former allies.
UUP leader Mike Nesbitt was accompanied by wife Lynda Bryans and son Peter as he voted at Gilnahirk primary school in east Belfast, while SDLP leader Colum Eastwood arrived at the Model Primary School in Londonderry with wife Rachael and his young daughter Rosa.
“It’s a dry day so hopefully that will mean a high turnout,” said Mr Nesbitt.
Mr Eastwood said: “This is a very important election. I think it’s probably the most important election since the Good Friday Agreement.”
Leader of the cross-community Alliance Party, Naomi Long, voted along with her husband, Michael, at St Colmcille’s parochial house in the east Belfast constituency where she was once MP. She smiled and shook hands with a voter as she left.
Polling stations opened at 7am and will close at 10pm.
The DUP and Sinn Fein have fallen out over the unionist party’s handling of a botched green energy scheme and a host of other issues.
Former DUP first minister Peter Robinson has warned politicians to step back and avert a headlong rush towards the destruction of devolved government.
If the three-week post-election deadline passes, Northern Ireland Secretary James Brokenshire is legally obliged to call yet another election.
But, in those circumstances, the Government may well move to pass emergency legislation to suspend devolution for the first time in 10 years.
While the Assembly election will not change how Theresa May’s Government treats talks to leave the European Union, the border between Northern Ireland and the Republic of Ireland is a key Brexit issue.
Five Assembly seats are up for grabs in 18 constituencies, with the overall number returned falling from 108 to 90.
A total of 228 candidates are running.
Former Sinn Fein deputy first minister Martin McGuinness resigned in January in protest over the DUP’s handling of the massively overspent Renewable Heat Incentive (RHI) scheme, which is paying grants to businesses worth more than the cost of running the wood biomass boilers.
That forced the dissolution of the institutions, which need nationalists and unionists in government to operate, and Mr Brokenshire called a snap election.
The next ballot had been due to take place in May 2021 after a poll last May.
Northern Ireland uses the single transferable vote (STV) proportional representation electoral system.
Counting will start during daytime on Friday with the last results not expected until later on Saturday.
All the main Stormont parties reduced the number of candidates fielded, in line with the downsized Assembly.
The largest party, the DUP, is running 38 - six fewer than last year.
Sinn Fein dropped five, from 39 to 34.
The UUP has 24 candidates - two fewer than in 2016 - while the SDLP is down three on 21.
The Alliance Party nominated 21 Assembly hopefuls, down two.