The S&P 500 was set for its worst day in a month on Monday as a more-virulent strain of the coronavirus in Britain sparked fears of fresh disruptions and offset optimism over a coronavirus aid package.
The strain, which is said to be up to 70% more transmissible than the original, forced many countries to shut their borders with the United Kingdom.
This shifted focus from a $900 billion coronavirus relief package, which is poised to be voted into effect by Congress later in the day. Anticipation of the bill had pushed Wall Street to record highs last week.
Electric-car maker Tesla Inc was among the biggest drags on the S&P 500, falling 4.8% from a record high in its first day of trading on the benchmark index.
"Optimism coming into this week was very high, and the markets were in need of a breather. You're going to see a bit of profit-taking between now and the end of the year," said Paul Nolte, portfolio manager at Kingsview Asset Management in Chicago.
Travel-related stocks marked big declines, with the S&P 1500 airlines index falling 2.6%. Cruise operators Royal Caribbean Cruises Ltd, Carnival Corp and Norwegian Cruise Line Holdings Ltd shed between 2.6% and 3.8%.
"The precautions required to assess the potential harm of the new Covid-19 strain will undoubtedly introduce additional risk to markets, which expected a smooth return to normal life following the vaccine's rollout," said James McDonald, chief executive officer of Hercules Investments in Los Angeles.
At 11:47 a.m. ET, the Dow Jones Industrial Average was down 159.59 points, or 0.53%, at 30,019.46, the S&P 500 was down 42.13 points, or 1.14%, at 3,667.28, and the Nasdaq Composite was down 118.72 points, or 0.93%, at 12,636.92.
The CBOE Volatility Index, also known as Wall Street's "fear gauge", jumped to its highest level since early November and was last at 25.96 points.
The S&P financials sector was the only S&P sector trading positive, thanks to gains in major lenders after the Federal Reserve permitted big banks to pay out dividends and buy back stock on a limited basis following a stress test.
Goldman Sachs Group Inc touched its highest level since April 2018.
Nike Inc jumped 5.1% following multiple price target raises after the athletic apparel maker boosted its full-year revenue forecast.
Lockheed Martin Corp fell 1.3% after it agreed to buy US rocket engine maker Aerojet Rocketdyne Holdings Inc for $4.4 billion. Shares of Aerojet climbed 22.3%.
International Business Machines Corp slipped 3% after saying it would acquire Finland-based startup Nordcloud, the latest in its series of deals focused on cloud computing.
Declining issues outnumbered advancers for a 3.16-to-1 ratio on the NYSE and for a 1.86-to-1 ratio on the Nasdaq.
The S&P index recorded seven new 52-week highs and no new lows, while the Nasdaq recorded 113 new highs and 14 new lows.