It's looking like another brutal day on Wall Street. US stocks moved sharply lower early Thursday following steep market declines all around the world, reports the AP. The Dow was down nearly 400 points about 11:30am Eastern, or 2.3%, while Nasdaq and the S&P 500 were off 1.5% and 1.9%, respectively, per MarketWatch. Investors are keeping a close eye on Janet Yellen's second day of testimony to Congress as part of her semiannual report. On Wednesday, the Fed chief cautioned that global weakness and falling financial markets could depress the US economy's growth. (More Dow Jones stories.)