Stocks tumbled from Hong Kong to Brazil, and US futures posted their steepest drop since 2001, on mounting speculation the world economy is slowing and company defaults will rise.

The MSCI World Index slumped the most since 2002, while Europe's Dow Jones Stoxx 600 Index sank 5.7 percent, pushing it into a bear market as Allianz SE and BNP Paribas SA slid. Hong Kong's Hang Seng Index had its biggest drop in six years.

"It's the worst I've ever seen," said Johan Stein, who helps manage the equivalent of about $14 billion at Nordea Asset Management in Stockholm. "The financial system is in terrible shape, and no one knows where this will end."

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