A UK exit from the EU in the context of Northern Ireland voting to Remain must prompt a poll on Irish unity, Sinn Fein has demanded.
While the republican party claimed the referendum will have "massive ramifications on the nature of the British state", given Scotland also voted Remain, the Democratic Unionists hailed the vote as set to deliver a bright future for Northern Ireland as part of an unshackled UK.
In Northern Ireland 440,707 (56%) people voted to Remain and 349,442 (44%) voted to Leave.
Of the region's 18 constituencies, 11 voted Remain and seven voted Leave.
A border poll can only be called by the region's Secretary of State in circumstances where there is clear evidence of a public opinion swing towards Irish unity.
Sinn Fein's national chairman Declan Kearney said the question of Northern Ireland remaining as part of the UK had now been brought into sharp focus.
"We have a situation where the north is going to be dragged out on the tails of a vote in England," he said.
"That is a huge democratic deficit for our society, building on the existing democratic deficit of partition.
"The British Government have now forfeited its mandate to represent the north of Ireland in relation to the European Union."
He added: "We now have a situation where Brexit has become a further cost of partition, a further cost of the Union and Sinn Fein will now press our demand, our long standing demand, for a border poll."
Supporters of the Stronger In campaign cheer as the EU referendum result from Gibraltar is announced at London's Royal Festival Hall.
Rob Stothard/PA Wire
The DUP's Sammy Wilson warmly welcomed the likely Brexit.
The East Antrim MP said the percentage of Brexit votes in Northern Ireland far exceeded polling predictions and insisted voters had not been taken in by Remain claims on the potential impact on free movement across the border.
"I am glad the people in Northern Ireland were not intimidated by the kind of nonsense that the Prime Minister and ex-prime ministers came off with - that the peace process was going to collapse, and World War Three was going to happen, and the economy was going to melt down, and the border was going to have gun towers and mine fields and barbed wire and machine gun posts and Lord knows what else along it," he said.
"People rose above that and many of them changed their minds and I am pleased about that."