NEW YORK — U.S. stock market indexes are trading above major round-number milestones.

The Dow Jones industrial average crossed 16,000 early Monday, dipped briefly, then rose again. The Standard & Poor’s 500 index, after piercing 1,800 in early trading, crisscrossed the milestone several times.

Stocks have been rising sharply this year as the U.S. economy improves, companies report bigger profits and the Federal Reserve keeps up its easy-money policies.

Investors are betting those policies are not likely to change soon. Janet Yellen, the nominee to succeed Ben Bernanke as Fed chairman, said in congressional testimony last week that she was prepared to keep interest rates low to stimulate the economy.

“The Fed is still pumping money into the system, which is helping fuel the market,” said Planned Financial Services CEO Frank Fantozzi. “There’s much more confidence in the market.”

The S&P 500 index has risen for six weeks straight and is up 26 percent so far this year. The market hasn’t risen that much in a whole year since 2003.

The S&P 500 has closed above major round-number milestones three times this year: 1,500 on Jan. 25, 1,600 on May 3 and 1,700 on Aug. 1.

At noon the S&P 500 was up 1.5 points, or 0.1 percent, at 1,799.

The Dow was up 43 points, or 0.3 percent, to 16,005.

Fantozzi said investors may also be nudging stocks up in reaction to news from the Chinese government Friday that it plans to open state industries to greater competition. Many big U.S. companies have come to rely on emerging markets like China to boost revenue. About half of the revenue in the S&P 500 comes outside the U.S.

In reaction to the China news, which was announced after Asian markets closed on Friday, China’s Shanghai Composite surged 2.9 percent and Hong Kong’s Hang Seng jumped 2.7 percent.

In the U.S., Boeing rose $2.43, or 1.8 percent, to $138.50, the most of the 30 stocks in the Dow. The plane maker booked $100 billion in orders at the opening of the Dubai Airshow.

Tyson Foods jumped 70 cents, or 2.4 percent, to $29.47, the most in the S&P 500 index. The food company said its net income surged 41 percent in the latest quarter on higher sales of beef and chicken. The company raised its dividend 50 percent.

The yield on the 10-year Treasury note fell to 2.68 percent from 2.71 percent.