U.S. stocks opened lower Wednesday, extending losses since the start of the week, as lingering worries over Ukraine's geopolitical tension and slowing Chinese growth weighed market sentiment.

The parliament of the autonomous republic of Crimea on Tuesday adopted a declaration of independence from Ukraine, which specifies that Crimea will become independent if its residents vote in favor of splitting from Kiev to join Moscow in Sunday's referendum.

U.S. President Barack Obama will meet with Ukraine's new Prime Minister Arseniy Yatsenyuk in Washington on Wednesday, according to the White House. Meanwhile, Western countries threatened to further sanctions on Russia.

The stock market continued to be pressured by China's weak trade data in February. China reported a large trade deficit in February mainly due to distortion by the Chinese New Year holidays, marking the first deficit since April 2013, China's official data showed on Saturday.

The economic calendar was light Wednesday, providing little direction to stocks.

U.S. mortgage applications last week slid 2.1 percent on a seasonally adjusted basis, said the Mortgage Bankers Association.

Shortly after the opening bell, the Dow Jones Industrial Average dropped 50.99 points, or 0.31 percent, to 16,300.26. The S&P 500 lost 7.49 points, or 0.40 percent, to 1,860.14. The Nasdaq Composite Index dropped 16.90 points, or 0.39 percent, to 4,290.29. Endi