NEW YORK » A strong morning rally for stocks turned into an afternoon sell-off on Wednesday, reminding investors that the market remains volatile.

Stocks started the day with sharp gains on optimism that policymakers in Asia will do more to help boost growth in the region. Japan’s stock market logged its biggest gain in almost seven years after comments from the country’s prime minister raised expectations of more measures to shore up economic growth.

The market then drifted gradually lower after a good-news-is-bad-news moment for investors. A government report released at midmorning showed that the number of available jobs jumped sharply in July to the highest level in 15 years. That added to evidence that hiring remains strong and may prompt Federal Reserve policymakers to raise interest rates at their next meeting later this month.

By the close, the Dow Jones industrial average had swung more than 400 points from its peak of the day. The index had surged a day earlier, logging its second-best day of the year.

The report "poured a bit of cold water on the market," said Karen Cavanaugh, a senior market strategist at Voya Financial. "We will definitely have some more volatility, but that’s part of a normal market."

The Dow ended 239.11 points, or 1.5 percent, lower at 16,253.57. The Standard & Poor’s 500 index dropped 27.37 points, or 0.8 percent, to 1,942.04. The Nasdaq composite fell 55.40 points, or 1.2 percent, to 4,756.53.

Job openings soared 8 percent to 5.75 million in July, the most since records began in 2000, the Labor Department said Wednesday. A separate report on Friday showed that U.S. unemployment fell to a seven-year low of 5.1 percent last month. If the hiring situation continues to improve it could potentially lead to higher wages and rising inflation.

Policymakers have held the Fed’s benchmark interest rates close to zero for almost eight years to help bolster the economy. The backdrop of low rates has been good for stocks, underpinning a 6 ½ year-long bull market. That dynamic may change if an improving economy pushes policymakers toward lifting rates for the first time in close to a decade.

"The Fed has been one of the main supports of the stock market and the economy," said Kate Warne, an investment strategist at Edward Jones. "It’s not a surprise that as it starts to move away from its extraordinary support that investors feel a bit nervous about what happens next."

Declines on Wednesday were led by energy stocks, which fell as the price of oil slumped for a third straight day.

Oil dropped on concerns that global supplies are still outpacing demand. U.S. crude fell $1.79 to close at $44.15 a barrel in New York. Brent crude, a benchmark for international oils used by many U.S. refineries, fell $1.94 to close at $47.58 in London.

At the open, investors had focused on some encouraging news out of Asia.

Japan’s Nikkei 225 soared after comments from Prime Minister Shinzo Abe that raised expectations of more measures to shore up economic growth under his "Abenomics" stimulus program. The Nikkei surged 7.7 percent, its biggest one-day rise since October 2008.

Investors were also comforted by comments from China’s No. 2 leader, who tried to ease concerns about the nation’s economic slowdown. Premier Li Keqiang said the nation’s growth is in the "proper range" and Beijing has no plans to allow its currency to decline further following the surprise devaluation on Aug. 11.

The devaluation spooked investors, who interpreted the move as an attempt to shore up an ailing economy. China is the world’s second-biggest economy and investors are worried that growth may be slowing more rapidly than previously thought. The stock market posted its worst monthly performance for more than three years in August.

Among individual stock movers on Tuesday, Barnes & Noble was a big loser.

The book retailers’ stock sank $4.50, or 28 percent, to $11.80 after the troubled bookseller reported a wider first-quarter loss as sales of its Nook e-reader and digital books fell sharply. Its college bookstore business, which was the only unit to post an increase in sales in the quarter, was spun off last month.

Netflix was the biggest gainer in the S&P 500 index.

The video streaming company snapped a seven-day losing streak, gaining $4.23, or 4.5 percent, to $99.18 after the company said it would bring its service to four more Asian countries next year.

In Europe, France’s CAC 40 advanced 1.4 percent. Germany’s DAX rose 0.3 percent. Britain’s FTSE 100 rose 1.3 percent.

In government bond trading, prices were little changed. The yield on the 10-year Treasury note held steady at 2.19 percent a day earlier. The dollar rose 0.2 percent against the euro to $1.1194 and gained against the yen, climbing 0.7 percent to 120.67.

The price of gold fell $19 to $1,102 an ounce. Silver fell 18 cents to $14.57 an ounce and copper edged up less than a penny to $2.44 per pound.

In other futures trading on the NYMEX:

— Wholesale gasoline fell 4.2 cents to close at $1.360 a gallon.

— Heating oil fell 5.5 cent to close at $1.539 a gallon.

— Natural gas fell 5.9 cents to close at $2.651 per 1,000 cubic feet.