Irish republicans are calling for the reunification of Ireland after Britain voted to leave the European Union.

The UK's decision means that a new era of border controls are likely to emerge between the two countries, despite Northern Ireland voting Remain by 56 per cent.

Northern Ireland has the only land frontier between the United Kingdom and the rest of the EU.

It was marked by military checkpoints until a 1998 peace deal ended three decades of sectarian violence.

Northern Ireland Deputy First Minister Martin McGuinness, right, and Sinn Fein President Gerry Adams, left, give their reaction to the EU Referendum vote at a press conference outside Stormont Castle

The decision means that a new era of border controls are likely to emerge between the two countries, despite Northern Ireland voting Remain by 56 per cent

Within minutes of the referendum outcome becoming apparent, Northern Ireland's largest Irish nationalist party, Sinn Fein, said the result intensified the case for a vote on whether Northern Ireland should leave the United Kingdom.

But, Stormont's First Minister has insisted Northern Ireland's place in the Brexiting UK is safe.

Martin McGuinness, the Sinn Fein leader, believes Irish people should be given a chance to vote on their future, saying there was a 'democratic imperative' to allow people to vote on reunification.

He said: 'If Britain votes to leave the European Union then that could have huge implications for the entire island of Ireland and, given all the predictions, would run counter to the democratic wishes of the Irish people.'

He added: 'The people of the north of Ireland have made it clear at the polls that they wish to remain in the EU.

‘This decision to drag us out of the European Union against our democratically expressed wishes has nothing to do with issues around the European institutions and everything to do with the civil war within the British Tory party.’

Sinn Fein chairman Declan Kearney said in a statement: 'This outcome tonight dramatically changes the political landscape here in the north of Ireland and we will be intensifying our case for the calling of a border poll.

'The British government as a direct result have forfeited any mandate to represent the interests of people here in the north of Ireland in circumstances where the north is dragged out of Europe as a result of a vote to leave.'

Britain's Secretary of State for Northern Ireland may call such a vote at any time, according to the 1998 agreement that brought about peace.

It also specifies that the Secretary 'shall' order a referendum if it appears likely that a majority of those voting would seek to form part of a united Ireland.

And Northern Ireland Secretary Theresa Villiers said she did not believe the criteria for triggering a border poll had been met.

Democratic Unionist leader Arlene Foster, who campaigned for an EU exit, said she was 'absolutely certain' the constitutional status was secure and claimed the Union was stronger after the Leave vote.

Of the region's 18 constituencies, 11 voted Remain and seven voted Leave.

Mrs Foster rejected the Sinn Fein demand, saying: 'The call for a border poll was as predictable as the flowers in May.

'We knew it would come but the test has not been met so therefore I don't believe it will happen.'

Arlene Foster, left, claimed the Union was stronger after the Leave vote, while Martin McGuinness, right, believes Irish people should be given a chance to vote on their future

The DUP leader added: 'I think we are now entering a new era of an even stronger United Kingdom.

'I am very much looking forward to working with our colleagues in our national government to build a very strong, outward-looking UK moving forward and of course Northern Ireland as a very key constituent part of that.'

The renewed focus on Northern Ireland's constitutional position comes as Scotland's First Minister Nicola Sturgeon said a second referendum on Scottish independence was 'highly likely'.

Nigel Dodds, a senior member of the province's largest party, the pro-British Democratic Unionist Party, also said that Sinn Fein were on very weak ground calling for a unity vote.

Ireland's Foreign Minister Charlie Flanagan said the reintroduction of a hard border would have to be considered in any negotiation and that the return of controls, for customs or security, could pose a difficult challenge for the peace process.

The dismantling of military border posts was a key aspect of a 1998 peace deal that ended three decades of violence, which took the lives of 3,600 people, between Catholic nationalists seeking a united Ireland and Protestant unionists who wanted to keep Northern Ireland British.

British finance minister George Osborne has said border controls would be inevitable, while former prime ministers Tony Blair and John Major, who also campaigned for a vote to Remain, said a Brexit could undermine peace in the six-county province.

Health Minister Michelle O'Neill, Sinn Fein leader Gerry Adams, Deputy First Minister Martin McGuinness and MEP Martina Anderson at Stormont Castle in Belfast

The border was marked by military checkpoints until a 1998 peace deal ended three decades of sectarian violence

Pro-Brexit campaigners, including Britain's minister for Northern Ireland, described those warnings as 'scaremongering' and said a Brexit would not endanger a common travel area that predates both countries' entry into the EU in 1973.

The presidents of the European Commission, Council and Parliament are to hold a joint press conference in Brussels to set out their initial response to the demand for Brexit.

And ministers in the Irish government were called to a special meeting to reflect on the result ahead of a statement by Taoiseach Enda Kenny.

A spokesman for the Dublin government said that the outcome 'clearly has very significant implications for Ireland, as well as for Britain and for the European Union. The government will meet later this morning to reflect on the result. Following that meeting, the Taoiseach will make a public statement'.

Sinn Fein president Gerry Adams travelled to Belfast to give his reaction to the vote.

Flanked by Stormont ministers and the party's MEP Martina Anderson outside a rain-soaked Stormont Castle, he said the decision would impact everyone north and south.

He said: 'This affects all of Ireland, whatever our attitude to the constitution or to the union or whatever. This affects everybody on this island.

'We all are part of a process of bringing about equality and change and harmony and reconciliation here and unless we are very careful a lot of the hard work that has been done, particularly around equality, rights, can be undone.'

Meanwhile, the party's deputy leader Martin McGuinness branded the referendum result a 'disastrous decision' which would have huge ramifications.

He said: 'What has happened overnight is massive with very profound implications.'

The customs stop between the Irish Republic and Northern Ireland on the road from Belfast to Dublin in 1950

Ireland is bracing itself for damaging economic and political fallout from the decision today, as the UK is its largest trading partner with imports and exports worth around £1billion each week.

The Republic has the EU's fastest-growing economy but also more to lose than any other member state from a 'Brexit' with far-reaching implications for its trade, economy, security of energy supplies and peace in British-ruled Northern Ireland.

Ireland's central bank had warned that a withdrawal would hurt economic growth and jobs and significantly impact the financial sector, while a government-commissioned report found it could cut trade with Britain by at least 20 per cent.

Services firm Noonan said earlier this week that an estimated cumulative Brexit-related hit on the Irish economy of as much as 1.6 percent of GDP would be 'containable'.

Irish exporters will be the first to suffer, as the pound weakened significantly against the euro, making their euro-priced goods more expensive.

Ministers in the Irish government were called to a special meeting to reflect on the result ahead of a statement by Taoiseach Enda Kenny

Today, there was a huge increase in searches of 'Irish passport' on Google from England, Scotland and Wales

Foreign Minister Flanagan said the country will have to consider taking steps to assist firms exporting into Britain.

Farmers and food producers, major UK suppliers, are especially vulnerable.

The Farmers Journal has said 50 per cent of Ireland's total beef exports goes to the UK, followed by one third of the country's total dairy exports.

With the UK leaving the EU, a drop in Irish exports of between £119m to £640m are to be expected.

The British Irish Chamber of Commerce said business needed a comprehensive and quickly concluded trade agreement between the EU and the UK that recognised the unique relationship between Ireland and the UK.

'As the voice of businesses with significant employment in the UK and Ireland, the Chamber is concerned about any adverse impact the UK's decision could have on trade between these Islands,' said John McGrane, Director General of the Chamber.

But the Republic could potentially try to benefit from Brexit, as some financial firms in the City of London may see Ireland as a lucrative option - an EU country, which is English-speaking and a close ally to the U.S.

Today, there was a huge increase in searches of 'Irish passport' on Google from England, Scotland and Wales.