Britain has voted to leave the European Union, the BBC said based on voter tallies from Thursday's referendum, an outcome that would set the country on an uncertain path and deal the largest setback to European efforts to forge greater unity since World War Two.
World financial markets dived as counting from 304 of 382 areas showed a 51.5/48.5 split for leaving. Sterling suffered its biggest one-day fall of 9.4 percent against the dollar on market fears the decision will hit investment in the world's 5th largest economy, raise questions over London's role as a global financial capital, and usher in months of political limbo.
The euro slumped nearly four percent against the dollar on concerns a ‘Brexit’ vote would do wider economic and political damage to what would become a 27-member union. Investors poured into safe haven assets including gold, and the yen surged.
In an early mark of international concern, Japan's top currency diplomat Masatsugu Asakawa said he would consult with Finance Minister Taro Aso on how to respond to the market moves, describing the foreign exchange moves as very rough.
Yet there was euphoria among Britain's eurosceptic forces, claiming a victory they styled as a protest against British political leaders, big business and foreign leaders including Barack Obama who had urged Britain to stay in the bloc.
"Dare to dream that the dawn is breaking on an independent United Kingdom," said Nigel Farage, leader of the eurosceptic UK Independence Party.
"If the predictions are right, 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."
He called the EU a "doomed project".
Asked if Prime Minister David Cameron, who called the referendum in 2013 and campaigned to stay in the bloc, should resign if Britain voted for Brexit, Farage said: "Immediately."
Quitting the EU could cost Britain access to the EU's trade barrier-free single market and mean it must seek new trade accords with countries around the world. President Barack Obama says it would be at the "back of a queue" for a U.S. pact.
The EU for its part will emerge economically and politically weakened, facing the departure not only of its most free-market proponent but also a member country that wields a U.N. Security Council veto and runs a powerful army. In one go, the bloc will lose around a sixth of its total economic output.
Cameron is expected to formally report the result to his European counterparts within days and prepare negotiations for the first exit by a member state from the EU -- an exit he has said would be irreversible.
The British leader called the referendum in 2013 in a bid to head off pressure from local eurosceptics, including within his own party. Initially billed as an easy ride, the vote has now put his political future on the line. Party ally Boris Johnson, the former London mayor who became the most recognizable face of the "leave" camp, is now widely tipped to seek his job.
Opinion polls had see-sawed throughout an acrimonious four-month campaign, but the Remain camp edged ahead last week after a pro-EU member of parliament, Jo Cox, was shot and stabbed to death. The attack shocked Britons and raised questions about whether the tone of the debate was fuelling intolerance and hatred.
In the end though, the pro-EU camp was powerless to stop a tide of anti-establishment feeling and disenchantment with a Europe that many Britons see as remote, bureaucratic and mired in permanent crises.