Supporters of the Stronger In Campaign react as results of the EU referendum are announced at the Royal Festival Hall, in London, Britain June 24, 2016. [Photo/Agencies]

"Dare to dream that the dawn is breaking on an independent United Kingdom," said Nigel Farage, leader of the eurosceptic UK Independence Party. "This will be a victory for real people, a victory for ordinary people, a victory for decent people ... Let June 23 go down in our history as our independence day."

Asked if Cameron, who called the referendum in 2013 and campaigned to stay in the bloc, should resign if Britain voted for Brexit, Farage said: "Immediately."

The United Kingdom itself now faces a threat to its survival, as Scotland voted 62 percent in favour of staying in the EU and is likely to press for a new referendum on whether to become independent after its 2014 vote to stay in the UK.

Scottish First Minister Nicola Sturgeon said Thursday's vote "makes clear that the people of Scotland see their future as part of the European Union."

Northern Ireland's largest Irish nationalist party, Sinn Fein, said the result intensified the case for a vote on whether to quit the United Kingdom.

European politicians reacted with shock. "Please tell me I'm still sleeping and this is all just a bad nightmare!" former Finnish Prime Minister Alexander Stubb tweeted.

The world's biggest trading bloc could even face an existential crisis as surging populist and anti-immigrant movements across the continent issue their own calls to quit. Far-right leaders in France and the Netherlands immediately demanded referendums of their own.

French National Front leader Marine Le Pen declared "Victory for freedom!". Dutch far right leader Geert Wilders said: "We want be in charge of our own country, our own money, our own borders, and our own immigration policy."