All trading at the New York Stock Exchange resumed at 3:10 p.m. EDT after unexpectedly halting trading for more than three hours Wednesday, due to an apparent technical issue. Reuters/Lucas Jackson

Trading resumed on the New York Stock Exchange just after 3 p.m. EDT Wednesday after unexpectedly stalling for nearly four hours, due to a technical issue. After trading restarted, the Dow (INDEXDJX:.DJI) was down 250.64 points for the day, or 1.42 percent, to 17,525.27. The S&P 500 (INDEXSP:.INX) dropped 33.08 points, or 1.57 percent, to 2,048.63. And the Nasdaq Composite (INDEXNASDAQ:.IXIC) dropped 85.15 points, or 1.7 percent, to 4,912.99.

Trading on NYSE and NYSE MKT resumed at the times above. NYSE

U.S. stocks were already trading sharply lower Wednesday ahead of the glitch. Investors continue to grapple with concerns that Greece will exit the eurozone, as well as the extreme volatility roiling China’s stock markets.

Trading stopped at the NYSE around 11:30 a.m. EDT, and the exchange said it was investigating the issue. “NYSE/NYSE MKT has temporarily suspended trading in all symbols. Additional information will follow as soon as possible,” the exchange said in a statement on its status page.

"We are currently experiencing a technical issue we’re working to resolve as quickly as possible,” the stock exchange said in a brief statement just after the halt. “Additional information will follow as soon as possible.”

Just before 12:30 p.m. EDT, the New York Stock Exchange said on Twitter that the source of the problem was "an internal technical issue and is not the result of a cyber breach."

The U.S. Securities and Exchange Commission issued a statement Wednesday saying the agency was "in contact with NYSE and [is] closely monitoring the situation and trading in NYSE-listed stocks. While NYSE is working to resolve the situation, NYSE and NYSE MKT stocks continue to trade normally through other trading venues."