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/ Source: NBC News

Will Greece default on its debt? Worries about that drove investors to unload shares on Friday, handing the major averages their worst day since March 25.

Stock markets were also shaken by news that China may tighten rules on borrowing to buy shares. After markets closed in Asia, Chinese financial regulators issued more warnings about that country's soaring stock market.

The Dow Jones industrial average plunged 250 points in midday trade, with General Electric the only gainer and American Express and 3M among the greatest decliners.

"I think what's more market moving (than domestic data) is Europe and concerns about Greece, and the put trading rules (in) China," Jim Meyer, chief investment officer at Tower Bridge Advisors.

The focus for European markets has been on Greek Finance Minister Yanis Varoufakis' visit to meet IMF officials, as investors become increasingly nervous about the funding crisis in Greece."I think that combination of a stronger euro and Greek chatter has profit-taking in the euro zone," said Art Hogan, chief market strategist at Wunderlich Securities.


-- CNBC, Reuters and NBC News Staff