By Noel Randewich

SAN FRANCISCO (Reuters) - Wall Street's worst week since 2008, sparked by fears about the fast-spreading coronavirus, has left almost half of the S&P 500's stocks in bear market territory, just nine days after the leading benchmark closed at a record high.

With the world preparing for a pandemic and investors increasingly fearing that the coronavirus could lead to a recession, the S&P 500 <.SPX> is on track to end the week down 13%, its worst week since 2008.

After closing at a record high on Feb. 19, the index has slumped 14%, now in a correction, but most of its individual components are in far worse shape.

"As severe as the decline has been, and even if most of the damage has been done, it's hard to believe it will be over in a week," Wellington Shields & Co market analyst Frank Gretz warned in a client note on Friday.

(Graphic: S&P 500 components plummet from 52-week highs - https://fingfx.thomsonreuters.com/gfx/mkt/13/2662/2627/Correction%20and%20bear.jpg)

Forty-seven percent of the S&P 500's components have fallen more than 20% from their 52-week highs, while another 51% have fallen more than 10%. Only about 10 S&P 500 stocks are down less than 10% from their highs, including healthcare companies Allergan and Quest Diagnostics , as well as Clorox , which has benefited from expectations of increased demand for its disinfectant cleaning products.

Investors consider securities or market indexes that have fallen 20% or more from their highs, and that maintain those declines for a sustained amount of time, to be in a bear market.

A drop of 10% is widely viewed as correction in a larger, ongoing rally, or bull market.

All of the S&P 500's 11 sectors have tumbled 10% or more from their year-highs, with energy's <.SPNY> 33% drop the worst among them, and the consumer staples' <.SPLRCS> sector's 11% decline the least.

(Graphic: S&P 500 sectors' declines from their 52 week highs - https://fingfx.thomsonreuters.com/gfx/mkt/13/2663/2628/Sectors.jpg)

As well, Wall Street's 10 most valuable companies have each tumbled by 14% or more. Of those, Apple and Mastercard have fallen the most, each down 19% from their 52-week highs, while Johnson & Johnson and Walmart are both down 14%, the group's smallest declines.

(Graphic: Performance of Wall St's most valuable companies - https://fingfx.thomsonreuters.com/gfx/mkt/13/2664/2629/Largest%20cos.jpg)

(Reporting by Noel Randewich; Editing by Alden Bentley and Nick Zieminski)