US stocks tumble amid new Greece doubts

US stock markets tumbled on Friday as new doubts surfaced over Greece's debt deal that just two days earlier seemed likely to go ahead.

Ending its worst week more than a month, the Dow Jones Industrial Average closed down 89.23 points (0.69 per cent) at 12,801.23.

The broad-based S&P 500 fell 9.31 (0.69 per cent) to 1,342.64, while the Nasdaq Composite dropped 23.35 (0.80 per cent) to 2,903.88.

The losses came as European leaders called for Athens to make tougher spending cuts while Greece's prime minister warned that the country faces "uncontrolled chaos" without a debt deal.

Meanwhile, a fall in China's imports and exports in January, while distorted by the lunar new year holiday, added evidence that the world's second-largest economy was slowing as the European and US economic weakness hurt demand for Chinese products.

An unexpected downturn in the University of Michigan's consumer sentiment index after several straight rises also raised doubts about the US economy's strength.

All but one of the 30 Dow Jones blue chips were down, led by a 3.3 per cent fall in Alcoa, which is sensitive to Chinese growth data, and a 1.8 per cent drop by DuPont.

The only gainer among the group was Home Depot, up 0.1 per cent.

Solar panel maker First Solar dropped 10.4 per cent after reporting a bureaucratic problem that endangered a plan to build a $US75 million ($A69.79 million) solar power project for power giant Exelon.

Bond prices gained as the US dollar surged on the new eurozone worries.

The yield on the 10-year Treasury fell to 1.97 from 2.05 per cent on Thursday, while the 30-year dropped to 3.12 per cent from 3.19 per cent.

Bond prices and yields move in opposite directions.

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