U.S. stock indices posted mixed results on Wednesday amid lower oil prices and Federal Reserve Chairwoman Janet Yellen remarks.

The Dow Jones Industrial Average declined 99.64 points, or 0.6%, to 15,914.74. The S&P 500 was almost unchanged at 1,851.86 (healthcare and technology were the only sectors to finish in the positive area with gains of 0.9% and 0.4% respectively). The Nasdaq Composite climbed 14.83 points, or 0.4%, to 4,283.59.

Janet Yellen admitted that financial conditions "have become less supportive to growth" and noted that the slowing economy of China had created risks. Nevertheless Yellen tried to defend the central bank's intension to raise rates and left the door open for further increases this year. Market participants are waiting for Yellen to speak to the Senate Banking Committee today.

This morning in Asia Hong Kong Hang Seng plunged 3.90%, or 753.17, to 18,535.00 after investors returned from a holiday. Analysts had expected a decline in Hong Kong stocks. Investors panicked amid ongoing declines in foreign stock markets and commodities.

Markets in mainland China and Japan are on holiday.