NEW YORK – Financial markets were jolted for a third day Wednesday by fears that a partial meltdown may have occurred at a nuclear plant in Japan. Stocks erased nearly all of their gains for the year.

The losses were broad. Each of the 30 stocks that make up the Dow Jones industrial average fell, with IBM Corp. and General Electric Co. losing the most. All 10 company groups in the Standard & Poor’s 500 index, the basis for most U.S. mutual funds, lost ground.

Stocks dropped sharply in midmorning trading after the European Union’s energy chief was quoted as saying that Japan’s nuclear crisis could get worse. Japan’s economy, the third-largest in the world after the United States and China, accounts for about 10 percent of U.S. exports.

Treasury prices jumped, sending yields to their lowest levels this year as investors piled into investments seen as being more stable. One measure of stock market volatility, the CBOE Market Volatility Index, jumped 18 percent in a sign that investors expect more wild swings.

“Investors are moving away from anything that has an element of risk with it because they don’t know what’s happening in Japan,” said Bill Stone, chief investment strategist at PNC Wealth Management.

The Dow Jones industrial average fell 242.12 points, or 2 percent, to 11,613.30.

It was the worst drop since Aug. 11. The Dow has now lost 3.6 percent in the past three days, its worst three-day loss since last July.

Japan temporarily suspended work at its stricken nuclear plant after a surge in radiation made it too dangerous for workers to remain there.