The Dow Jones industrial average rose 147 points, or 0.9 percent, to 16,646 as of 9:35 a.m. Eastern time Wednesday.
The Standard & Poor's 500 index climbed 17 points, or 0.9 percent, to 1,986. The Nasdaq composite rose 46 points, or 1 percent, to 4,857.
Japan's market jumped the most in almost seven years as investors hoped for more stimulus measures. Markets in China and Europe also rose sharply.