Stormont's First Minister has expressed hope of a high turn-out in the North as voters continued to cast their ballots in the EU referendum.
Arlene Foster, a Brexit campaigner, said it was important that those on both sides of the debate made their voices heard.
"I understand there has been a good turn-out in some of the areas where previously there hasn't been so far - so that's good to hear," she said.
The Democratic Unionist leader added: "Everyone has the opportunity to cast their vote today and I hope they take that opportunity, regardless of what that might be, because this is a huge opportunity for all the citizens of the United Kingdom to make their voices heard in terms of the European Union."
Sinn Fein president Gerry Adams, a Remain advocate, also encouraged people to get out and vote.
"Come out and vote, if you haven't voted there is still time, vote to remain - it's not in Ireland's interests to do anything else," he said.
Polling stations opened at 7am and will close at 10pm. The count will begin shortly after the 600-plus stations close.
There will be a count for each of the region's 18 parliamentary constituencies, with those separate outcomes added together for an overall Northern Ireland result.
Counting will be conducted in eight centres across the region, with the main result expected to be announced at the Belfast count at about 4am.
Sinn Fein, the Ulster Unionists, the SDLP and Alliance Party campaigned for a Remain vote in the referendum campaign while the DUP, Traditional Unionist Voice and Ukip were among those advocating a Brexit.
The future of the Irish border was a key issue in the campaign, with claim and counter claim on whether a UK exit would see a return to security and customs checkpoints.