Britain voted to break away from the European Union, toppling Prime Minister David Cameron and dealing a thunderous blow to the 60-year-old bloc that sent world markets plummeting on Friday.
Cameron announced he would step down to make way for a new leader by early October after voters opted to exit the 28-nation alliance in defiance of his predictions of economic disaster and isolation.
Britons, many of them worried by immigration, decided 52 percent to 48 percent in favour of quitting the bloc, a margin of more than one million votes, according to final results from Thursday's referendum.
"The British people have voted to leave the European Union and their will must be respected," Cameron said, as the shockwave of their decision sent sterling, global stocks and oil prices plummeting.
Britain will be the first country to leave in the history of the EU, the culmination of decades of suspicion over European aims of creating an ever-closer political union.
The result -- after a deeply polarising and often vitriolic campaign -- also threatens the very unity of the United Kingdom, with Scotland unwilling to follow the rest of the country out of the EU.
The Conservative prime minister promised to try to "steady the ship" over the next few months but said a new leader should be installed by early October.
"I do not think it would be right for me to try to be the captain that steers our country to its next destination," he said outside his official Downing Street residence in London.
The bookmakers' favourite to replace him is former London mayor Boris Johnson, a rival from within his ruling Conservative Party who was the "Leave" camp figurehead.
"Let June 23 go down in our history as our independence day," said top anti-EU campaigner Nigel Farage, leader of the UK Independence Party, who had promised Britons the chance to retake power from Brussels and rein in high immigration.
"We've done it! We've won!" anti-EU campaigners shouted at the festivities in an office block in Westminster, popping open champagne bottles as "Leave" victories flowed in. "Out! Out! Out!", they chanted as dawn broke.
Immigration and an erosion of financial security have become rallying cries for populists across Europe, just as they have for Donald Trump's campaign in the US presidential election.
Trump hailed the British vote as he arrived in Scotland to unveil a refurbishment of his Trump Turnberry golf course, shortly after the results became clear. "I think it's a great thing. I think it's a fantastic thing," he told reporters.
The result of the vote sent sterling collapsing 10 percent to touch a 31-year low of $1.3229. European stock markets dropped around eight percent at the opening bell. British banking shares lost a quarter of their value in morning trade.
The Bank of England promised to take "all necessary steps" to secure market stability.
"It's a madhouse in here. It has been a bloodbath. Carnage," said David Papier, head of sales trading at foreign exchange house ETX Capital in London.
Voters appeared to have to shrugged off warnings that a Brexit would create a budget hole requiring spending cuts and tax increases once they lose unfettered trade access to the EU.
Their decision will reawaken fears of a domino-effect ripple of exit votes in eurosceptic member state that could imperil the integrity of the bloc, already struggling with twin economic and refugee crises.
Dutch far-right MP Geert Wilders and French National Front leader Marine Le Pen immediately called for referendums on EU membership in their own countries.
"The eurosceptic genie is out of the bottle and it will now not be put back," Farage said.
The referendum means the world's fifth-largest economy must now go it alone in the global economy, launching lengthy exit negotiations with the bloc and brokering new deals with all the countries it now trades with under the EU's umbrella.
European Commission chief Jean-Claude Juncker has warned the EU will "not be bending over backwards" to help Britain in those negotiations. Analysts say it could take the island nation a decade to secure new trade accords worldwide.
"It looks like a sad day for Europe and the United Kingdom," German Foreign Minister Frank-Walter Steinmeier said on Twitter.
In a worst-case scenario, the International Monetary Fund has warned that the British economy could sink into recession next year and overall economic output would be 5.6 percent lower than otherwise forecast by 2019, with unemployment rising back above six percent.
Split in two
Thousands of jobs in the City could be transferred to Frankfurt or Paris, top companies have warned. The Brexit camp argued that the business world will adapt quickly, however, with Britain's flexible and dynamic economy buoyed by new economic partners and selective immigration.
The campaign has left Britain riven in two, marked by the brutal murder of pro-"Remain" British lawmaker Jo Cox, a mother of two who was stabbed, shot and left bleeding to death on the pavement a week ahead of the vote.
Two years after Scotland voted in a referendum to remain in the United Kingdom, its political leader First Minister Nicola Sturgeon has said a new independence vote is "definitely on the table" after Britain voted against the majority will expressed by Scots.
"Scotland sees its future as part of the EU," Sturgeon told television news after the vote.
Northern Ireland, which is part of the United Kingdom, is now faced with the prospect of customs barriers for trade with EU-member the Republic of Ireland. Irish republicans Sinn Fein called for a vote on Irish unity following the referendum.
Leaders of the European Union, a bloc born out of a determination to forge lasting peace after two world wars, will open a two-day summit on Tuesday to grapple with the British decision.