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Greek Finance Minister Varoufakis has resigned, and Greeks are waiting to hear from the ECB Monday about funding to the country, reports CNBC's Michelle Caruso-Cabrera.
CNBC's Eunice Yoon reports China authorities rolled out emergency measures to stop the market selloff.
Overseas markets tumbled, as did U.S. stock futures, after Greece voters overwhelmingly rejected the terms of a proposed bailout. Wall Street faced an extension of recent losses.