Fear is spreading in the stock market.

A monthlong drop in U.S. stocks intensified in afternoon trading Wednesday, sending the Dow Jones industrial average down more than 450 points and putting the index on track for its biggest loss in more than a year.

The decline came as investor fears of a global economic slowdown deepened after several weeks of turbulent market action. Worrisome economic news in the U.S. also fueled Wednesday's selling.

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Traders dumped risky assets and parked their money in investments seen as relatively safe, such as U.S. government bonds. That pushed the yield on the 10-year Treasury note briefly below 2 percent, the lowest level in more than a year.

"It's a function of the U.S. being the best house in a bad neighborhood," said Terry Sandven, chief equity strategist at U.S. Bank Wealth Management. "There's still uncertainty about economic growth, primarily on a global basis."

Stocks plunged at the open of trading and extended a rough October for the market.

The Dow was down 299 points, or 1.8 percent, to 16,016 as of 3:17 p.m. Eastern time. It dropped as much as 460 points earlier and was headed for its biggest percentage drop since June 2013.

The Standard & Poor's 500 index fell 31 points, or 1.7 percent, to 1,846. The Nasdaq composite dropped 52 points, or 1.2 percent, to 4,176.

All three indexes are now down for the year.

Until late September, the market had moved higher for most of 2014 as U.S. corporate earnings kept up record growth and the economy strengthened.

Stocks, though, have been declining for nearly a month as investors have grown increasingly nervous about slowing global growth. While the U.S. economy remains healthy, investors are concerned that earnings growth will fade this year and next because of the slowdown in Europe and, to a lesser degree, China.

Wednesday's slide brings the stock market closer to a correction. That happens when a benchmark index like the S&P 500 falls 10 percent or more from a recent peak.

The S&P 500 hit its most recent peak of 2,011.36 on Sept. 18. It would have to close at 1,810.22 to mark a correction. The last time that happened was October 2011.

The correction threshold for the Dow is 15,551. The Nasdaq's is 4,138. The Nasdaq traded below that threshold on Wednesday and could match the widely accepted definition of being in a correction if it closes below that point.

Parts of the market are already in correction, which has some analysts calling for caution. Small-company stocks, as measured by the Russell 2000 index, have fallen 12.8 percent since hitting a peak in July and are down 9.5 percent for the year.

Many market watchers say occasional corrections are a healthy phenomenon over the long term and give investors an opportunity to add to their holdings at a lower cost.

"That's why it' so important to stay invested at a time like this, rather than think it's a time to get out," said Kate Warne, an investment strategist at Edward Jones.

Bond prices soared Wednesday as investors shifted money into safe-haven investments.

Early on, the yield on the 10-year Treasury note plunged to 1.91 percent from 2.20 percent the day before, or 29 basis points, a huge move. It recovered to 2.06 percent in afternoon trading. Bond yields fall when their prices rise.

"It typically takes weeks for 10-year Treasurys to move 29 basis points," noted Tom Di Galoma, head of fixed income rates in New York at ED&F Man Capital. "Today it moved 29 basis points in 5 minutes."

Investors got discouraging U.S. economic news early Wednesday, when the Commerce Department reported that retail sales declined 0.3 percent in September from the previous month. Purchases of autos, gasoline, furniture and clothing slowed.

Retail sales have risen 4.3 percent over the past 12 months, slightly below their historical pace.

A snapshot of manufacturing activity didn't bolster optimism.

The Federal Reserve Bank of New York's Empire State Manufacturing index dropped sharply from 27.5 to 6.2 in October as new orders shrank and shipments barely rose. The latest reading marks the slowest pace of growth in six months.

All 10 sectors in the S&P 500 declined, led by financial stocks, which slid 3.3 percent.

KeyCorp, Hudson City Bancorp, Lincoln National and Citigroup were among the biggest decliners. Covidien led the slide among S&P 500 companies, falling $7.89, or 8.5 percent, to $84.46.

Bucking the trend were several energy and oil services companies, including Cabot Oil & Gas, Southwest Energy and Helmerich & Payne. Southwestern paced the gainers, rising $2.02, or 6.1 percent, to $35.12.

Homebuilders surged, getting a lift from the slide in the 10-year Treasury bond yield, which affects rate on consumer and business loans. A decline in the 10-year Treasury note yield should nudge mortgage rates lower, spurring home sales.

M/I Homes got the biggest boost among the builders, adding 77 cents, or 4 percent, to $19.99.

As more companies report earnings over the next couple of weeks, investors should get a better read of the impact that the economic situation overseas will have on U.S. companies.

In overseas market action, traders worried that Europe might relapse into recession.

France's CAC 40 sank 3.6 percent and Germany's DAX lost 2.9 percent. Britain's FTSE 100 fell 2.8 percent. Greece's stock index plunged 6.3 percent on concerns that the Greek government could collapse next year, putting its bailout program in danger. The index fell 5.7 percent the previous day.

U.S. crude slipped 23 cents to $81.61 a barrel.

In metals trading, gold rose $10.50 to $1,244.80 an ounce, silver rose six cents to $17.46 an ounce and copper fell eight cents to $3.01 a pound.