The electorate is returning to the polls to select a new devolved legislature for the second time in less than a year.
Power-sharing arrangements between the two largest parties at Stormont - the Democratic Unionists and Sinn Fein - collapsed in January.
If post-election talks cannot mend tensions between the former coalition partners then direct rule from London is on the cards.
An alternative cross-community partnership of the Ulster Unionists and nationalist Social Democratic and Labour Party (SDLP) is bidding to wrest control away from the fractious former allies.
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 first minister Peter Robinson has warned politicians to step back and avert a headlong rush towards the destruction of devolved government.
While the vote 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 could become an issue in how Brexit is introduced.
MORE: Everything you need to know about voting in the Assembly elections
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 Northern Ireland Secretary James 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.