World stock markets have tumbled as investors worry about the health of the US economy after the Federal Reserve warned that the recovery was likely to be "more modest" in the short term.
The Dow Jones opened 196 points lower, while European markets were down 2%.
On Tuesday, the Fed said it would use proceeds from investments in mortgage securities to buy long-term government debt, to try to bolster the economy.
Separately, data showed the US trade deficit rose to a 20-month high.
The Commerce Department said the deficit widened to $49.9bn (£31.9bn) in June, which surprised economists who were expecting a smaller trade gap.
Weakening dollar
Earlier, Asian markets had set the tone for traders elsewhere by falling, with news that China's industrial growth slowed further in July also hitting sentiment.
Japan's Nikkei 225 index closed 2.7% lower at 9,293, while Hong Kong's Hang Seng index shed 179 points to close at 21,294.
In afternoon trading in Europe, leading share indexes in London, Paris and Frankfurt were all down by more than 2%.
The Fed's assessment of the US economy also put more pressure on the dollar, which hit a 15-year low against the yen.
The US currency fell to 84.73 yen, the lowest level since 5 July 1995, before it later pulled back to stand at 85.25 yen.
But the pound weakened against the dollar after the Bank of England warned that the UK faced "a choppy recovery" and downgraded its growth forecasts.
Analysts said the Bank's Inflation Report suggested that interest rates were likely to remain low for some time.
