"Liquidation is under way across equities and commodities, sparked by fears that the global economy is set to slow," Andrew Wilkinson, chief economic strategist at Miller Tabak & Co in New York, told Reuters.
Commodities including gold, silver, palladium and oil declined. Gold, already in a bear market, plunged more than 9 per cent today, while silver tumbled more than 11 per cent.
The slide in gold, with spot gold touching a two-year low of US$1,384.69 an ounce, is set to continue.
"We are entering a phase of additional long liquidation by ETF [exchange-traded-funds] investors and short-selling from hedge funds, which will continue in the foreseeable future," Saxo Bank senior manager Ole Hansen told Reuters.
Donald Selkin, who helps manage about US$3 billion of assets as chief market strategist at National Securities in New York, agrees.
"The perception is that gold is not really needed as a safe haven," Selkin told Bloomberg. "People are looking at the stock market and they're stunned, and there's no inflation. So people are saying 'What do we need gold for?'"
In Europe, the Stoxx 600 Index ended the day with a 0.7 per cent decline from the previous close. Benchmark stock indexes in Frankfurt, Paris and London closed lower too, down 0.4 per cent, 0.5 per cent and 0.6 per cent respectively.
There was some good news. Citigroup posted better-than-expected profit, bolstering its shares, last up 1.45 per cent.