The British pound crashed to its lowest levels in 31 years as the country voted to leave the European Union in a historic referendum.
The pound dropped below $1.35 for the first time since 1985. The currency fell 11% and was on course for its biggest one-day fall ever. It was down against all major world currencies.
Stocks markets around the world are also falling sharply.
With more than 70% of the votes counted, CNN predicted that the campaign to leave the EU would win Thursday's referendum.
"It is vile and ugly out there, the British pound is facing its worst day ever," said Naeem Aslam, chief market analyst at ThinkForex.
Economists have been warning for months that if the U.K. referendum resulted in a vote for a British exit (Brexit) from the EU, that would do lasting damage to the British economy.
"Day after day, we looked up and worried that the sky might fall on our heads. And then one day.... it did," tweeted Kit Juckes, strategist at Societe Generale.
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The pound swung wildly during the referendum campaign in response to opinion polls.
It even reached $1.50 overnight as investors grew increasingly confident the U.K. would vote to stay in the bloc.
But that changed rapidly as preliminary results from the vote were declared.
"What we're seeing now is the market reacting with complete shock and bewilderment as the results unfold," said Trevor Charsley, analyst at AFEX.
"Investors were not prepared for this and this is what you get when you have premature celebrations."