By Anora Mahmudova, MarketWatch

NEW YORK (MarketWatch) -- U.S. stocks moved sharply lower on Wednesday, briefly erasing the previous day's modest gains, after a report on the services sector failed to repair sentiment bruised by a weak ADP jobs report.

As volatility has been rising steadily, some analysts say the main indexes are in a midst of a correction and have further to fall. The Dow Average is down more than 7% from its peak. The benchmark S&P 500 is down 5.7% from its all-time high.

The S&P 500 (SPX) fell 12 points, or 0.7%, to 1,743.20. The Dow Jones Industrial Average (DJI) shed 48 points, or 0.3% to 15,398.13. The Nasdaq Composite (RIXF) dropped 47 points, or 1.2% to 3,983.86.

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Stocks fell to session lows after the Institute for Supply Management said U.S. service-sector companies expanded in January at a slightly faster pace, a survey of executives found. The employment gauge also ticked up, marking the highest level in more than three years.

Stocks had opened lower after Automatic Data Processing Inc. said private-sector-employment gains slowed down in January, with employers adding 175,000 jobs, slightly less than expected, while the December number was revised down to 227,000. The report comes ahead of the official non-farm payrolls data due on Friday.

"Even though it was the emerging markets that triggered recent selling, concerns have shifted to the U.S. economy and recent data have been disappointing," said Nicholas Colas, chief market strategist at ConvergEx Group, a global brokerage company based in New York.

"Volatility has moved to 'old normal' levels, which means more downturns in near future as we are in the midst of a correction," Colas said.

"Money outflows year-to-date have been quite big, as investors withdrew $22.5 billion from all U.S. listed ETFs, most of it from the highly liquid SPDR S&P 500 ETF Trust (SPY). We had a big rally last year and it is time to pay some of that back, which is normal in the markets," he added.

Implied volatility on the S&P 500 as measured by the CBOE Vix index rose to 20, which is close to the 30-year average.

Investors will be paying attention to two Fed officials speaking today for clues about changes in monetary policy. Philadelphia Fed President Charles Plosser is due to speak on the economy at 12:30 p.m. Eastern Time in Rochester, New York, and Atlanta Fed President Dennis Lockhart is scheduled to speak on the economic outlook at 1:40 p.m. Eastern Time in Birmingham, Alabama.

Shares of C.H. Robinson Worldwide Inc. (CHRWD) fell sharply after the company posted a 64% drop in fourth-quarter profit on Tuesday, missing expectations.

CVS Caremark Corp. (CVS) shares fell after the drugstore chain said Wednesday it would stop selling cigarettes and tobacco products in stores by Oct. 1. CVS said the estimated $2 billion drop in revenues would not affect 2014 per-share earnings.

Shares in Genworth Financial Inc. (GNW) rallied after the company reported a 24% rise in fourth-quarter profit, beating expectations.

Humana Inc. (HUM) shares slid after the health insurer said it swung to a fourth-quarter loss, but stuck to its 2014 earnings guidance.

Merck & Co. Inc.(MRK) shares rose after the company said it entered three separate collaboration agreements with peers to evaluate its investigational immunotherapy cancer treatment. Earlier, the company announced a drop in fourth-quarter profit and revenue missing expectations.

Shares in Tableau Software Inc. (DATA) and Myriad Genetics Inc. (MYGN) soared after upbeat quarterly results late Tuesday.

Twitter Inc. (TWTR) and Walt Disney Co. (DIS) will release results after the market close.

In other markets, European stocks erased gains after the ADP report. Stocks stabilized in Asia. Gold and oil prices moved higher, while the dollar extended losses after a report on private-sector employment showed a slower pace of growth than expected.

More stories from MarketWatch:

Greenhaus: S&P pullback is 'normal' so far

8 stock indexes around the globe facing corrections

Volatility Index raises caution flag for market bears

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