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Signs the US Federal Reserve might soon begin trimming its stimulus programme sparked falls in world shares on Wednesday, while a new Bank of England policy lifted sterling by changing expectations for a rate rise.
US stock index futures pointed to Wall Street extending the share selloff, which was triggered when two Fed officials suggested the central bank may reduce the pace of bond purchases as early as next month, depending on economic data.
"We're going to get tapering, it's really a question of when, and not if, and that's why we've seen a decline in (equity) markets," said Michael Hewson, market analyst at CMC Markets.
The comments led to MSCI's main Asian ex-Japan index hitting its lowest levels since mid-July and sent the broader MSCI world equity index down 0.5% to put it on course for its worst day in five weeks.
Europe's broad FTSE Eurofirst 300 index had also shed 0.1% though it was off its lows after data showed German industry output had rebounded in June - further evidence that Europe's largest economy is gaining momentum.
In Britain, central bank governor Mark Carney, in his first policy move since taking over last month, outlined a new framework for setting interest rates, triggering a wave of volatility in London's financial markets.
Carney said UK rates would be kept at a record low of 0.5% until unemployment falls to 7%, something unlikely for another three years. He also made any move conditional on inflation staying low and the financial system being stable at the time.
Traders reacted to the policy by bringing forward slightly expectations of when the first UK interest rate rise may occur, given the raft of strong economic data in the past few weeks.
Sterling, which initially lost ground on the low rates' promise, hit a peak of $1.5493, its highest since June 21 before settling at $1.5446, up 0.7%.
"A line in the sand has been drawn for a possible 2016 horizon (for a rate rise). Previously the market had not known this and it could have been even longer maybe, so traders have now got to factor this in now," said Central Markets chief strategist Richard Perry.
Britain's main FTSE 100 index however moved in the opposite direction, extended its losses to fall 0.8% after Carney spoke.
British government bond futures also reversed initial losses to be little changed.
TAPER TALK
The speculation over an early cutback in the Fed's bond buying plans was supporting the dollar against most emerging market currencies and a basket of major developed world currencies with the notable exception of the yen.
In Tokyo, capital inflows linked to interest payments on the country's massive US Treasury holdings and the ongoing retreat by Japanese investors from slowing Asian economies, combined with the growing risk aversion to lift the yen sharply.
The dollar touched a one-and-a-half month low against the yen 96.76 yen, before settling at 97.10 yen, down 0.7%.
The stronger yen added to the negative tone in Tokyo share markets to send the Nikkei index tumbling 4% for its biggest one-day%age loss since mid-June.
In commodity markets, gold was at three-week low as any tapering would support a higher interest rate environment that diminishes the precious metal's attractiveness.
"It does very much look as though the Fed is keen to go ahead with its tapering, perhaps starting as soon as September and that has added a little negative sentiment to the gold market and for that we think there is more downside risk in the near term," Natixis analyst Nic Brown said.
Copper slipped 1.2% to $6,914 a tonne, giving back most of the gains made on Tuesday while Brent crude fell below $108 per barrel, dropping for a fourth session and logging its longest losing streak since April.
