(Reuters) - Technology shares -- a key engine of the stock market’s climb to records over the last several months -- are now among those leading Wall Street’s plunge on growing concerns over the coronavirus outbreak.

FILE PHOTO: A view of the exterior of the Nasdaq market site in the Manhattan borough of New York City, U.S., October 24, 2016. REUTERS/Shannon Stapleton/File Photo

The S&P 500 information technology sector has fallen 9.3% since Thursday’s close, outpacing a drop of 7.3% for the broader index. Only energy has performed worse, reflecting a sharp decline in oil prices on fears that the coronavirus will slow global economic activity.

Investors poured billions into big technology stocks and other momentum bets last year, as a dovish Federal Reserve stoked risk appetite and fueled a rally of more than 30% in the S&P 500. Some big technology and momentum stocks kept griding higher, driving markets to records even as concerns grew over the virus’ spread in China in recent weeks.

Now a surge in coronavirus cases outside of China has made some investors more willing to part with riskier assets in favor of traditional havens like gold and U.S. Treasuries, which have soared in recent days.

“Everyone just got a full helping of tech stocks up at the high. It was some of the most reckless buying I’ve seen in my lifetime,” said Christopher Stanton, chief investment officer at Sunrise Capital Partners.

(GRAPHIC: Roller coaster 2020 for market's big names - )

Stanton rode shares of Amazon and other big technology names higher last year. He now owns derivatives will rise if the tech-heavy Nasdaq Composite index continues to decline.

As of Friday, the S&P 500 information technology sector accounted for nearly 55% of the overall S&P 500’s total return in 2020, even though the sector was only 24.3% of the benchmark index’s market value, according to Howard Silverblatt, senior index analyst at S&P Dow Jones Indices.

Just four companies -- Microsoft, Apple, Amazon and Google-parent Alphabet -- accounted for 46.4% of the 2020 total return as of Friday, Silverblatt said.

That magnitude of concentration in a small universe of names had some investors worried that they have become overstretched and vulnerable to a sudden reversal in risk appetite. The tech sector’s valuation recently stood at its highest forward price-to-earnings multiple since 2004, according to Refinitiv Datastream.

And while technology stocks have tended to outperform during good times, they can also fall further than broader markets when risk appetite dries up. When the S&P 500 tumbled nearly 20% from its high in late 2018, the tech sector suffered a steeper 23% drop over that period.

“Up until now, this market has been remarkably free of any critical thinking,” said Hans Olsen, chief investment officer of Fiduciary Trust Company. “This has given investors a perfect reason to examine what they are paying and what they are expecting.”