"These would be large, massive shocks where you would not know what the consequences would be," he told reporters.
Asked about what additional steps the ECB could take to address the economic situation, he pointed out the ECB had already taken significant steps that needed time to show their impact.
Among earnings, Hewlett-Packard rallied after the Dow component beat on earnings and announced plans to lay off 27,000 employees, or 8 percent of its workforce. Its third-quarter outlook fell short of expectations but its full-year topped the consensus. At least three brokerages raise their price target on the firm.
NetApp plunged after the computer storage and data management company's guidance disappointed and the CEO warned of uncertainty in Europe. At least eight brokerages cut their price target on the firm.
Costco rose after the warehouse club operator posted better-than-expected earnings .
Tiffany slumped after the upscale jewelry retailer lowered its guidance, hurt by slowing economic global growth.
The U.S. Treasury is set to auction $29 billion in 7-year notes on Thursday, with the results scheduled to be available shortly after 1:00 p.m.
—By CNBC’s JeeYeon Park (Follow JeeYeon on Twitter: @JeeYeonParkCNBC )
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