More than $US2 trillion ($A2.63 trillion) has been wiped off the value of world stocks as Britain's vote to leave the European Union triggered 5-10 per cent falls across Europe's biggest bourses and a record plunge for sterling.
Such a body blow to global confidence could prevent the US Federal Reserve from raising interest rates as planned this year, and might even provoke a new round of emergency policy easing from all the major central banks.
Risk assets were scorched as investors fled to the traditional safe-harbours of top-rated government debt, Japanese yen and gold.
Almost $US1 trillion had been lost from European share prices ahead of what is expected to be a nearly 4 per cent fall on Wall Street when it opens later.
London's FTSE dropped almost 5 per cent on Friday while Frankfurt and Paris fell 6 to 8 per cent.
Italian, Spanish and European bank stocks all headed for their sharpest one-day drops ever.
Worries that other EU states could hold their own referendums were compounded by the fact that markets had rallied on Thursday, seemingly convinced the UK would vote to stay in.
Britain's big banks took a $US100 billion battering, with Lloyds, Barclays and RBS plunging as much as 30 per cent at one point.
The British pound dived by 18 US cents at one point, easily the biggest fall in living memory, to hit its lowest since 1985. The euro in turn slid 3 per cent to $US1.1050 as investors feared for its very future.
Having campaigned to keep the country in the EU, British Prime Minister David Cameron announced he would step down.
Results showed a 51.9/48.1 per cent split for leaving, setting the UK on an uncertain path and dealing the largest setback to European efforts to forge greater unity since World War II.
More angst came as Scotland's first minister said the option of another vote for her country to split from the UK - rejected by Scottish voters two years ago - was now firmly on the table.
Sterling sank a staggering 10 per cent at one point and was last down 8 per cent at $US1.3667, having carved out a range of $US1.3228 to $US1.5022. The fall was even larger than during the global financial crisis and the currency was moving two or three cents in the blink of an eye.
"It's an extraordinary move for financial markets and also for democracy," said co-head of portfolio investments of London-based currency specialist Millennium Global Richard Benson.
"The market is pricing interest rate cuts from the big central banks and we assume there will be a global liquidity add from them," he added.
That message was being broadcast loud and clear. The Bank of England, European Central Bank and the People's Bank of China all said they were ready to provide liquidity if needed to ensure global market stability.
The shockwaves affected all asset classes and regions.
The safe-haven yen sprang higher to stand at Y102.15 per US dollar, having been as low as Y106.81 at one stage. The US dollar's peak decline of 4 per cent was the largest since 1998.
That prompted warnings from Japanese officials that excessive forex moves were undesirable. Traders said they were wary of being caught with exposed positions if the global central banks chose to step in to calm the volatility.
Emerging market currencies across Asia and eastern Europe and South Africa's rand all buckled on fears that investors could pull out. Poland, home of eastern European immigrants to Britain, saw its zloty slump 5 per cent.
Europe's natural safety play, the 10-year German government bond, surged to send its yields tumbling back into negative territory and a new record low.
MSCI's broadest index of Asia-Pacific shares outside Japan slid almost 5 per cent, while Shanghai stocks lost 1.1 per cent.
Financial markets have been gripped for months by worries about what a British exit from the EU would mean for Europe's stability.
"Obviously, there will be a large spill-over effects across all global economies ... Not only will the UK go into recession, Europe will follow suit," predicted Matt Sherwood, head of investment strategy at fund manager Perpetual in Sydney.
Investors stampeded into low risk sovereign bonds, with US 10-year Treasury futures jumping over 2 points in Asian hours, an unusually large move. Yields on the cash note fell 25 basis points to 1.48 per cent, the steepest one-day drop since 2009 and the lowest yield since 2012.
The rally even extended to UK bonds, despite a warning from ratings agency Standard & Poor's that it was likely to downgrade Britain's triple-A credit rating if it left the EU.
Yields on benchmark 10-year gilts fell 27 basis points to 1.108 pct.
