Wall Street has ended sharply lower as US coronavirus infections surge and investors weigh the timeline for the mass rollout of an effective vaccine.
New York became the latest state to introduce stricter social distancing rules on Wednesday, as new infections in the country surged above 100,000 for an eighth consecutive day.
The blue-chip Dow was pulled down by industrial and financial companies sensitive to economic growth, with Boeing Co and Goldman Sachs down 3 per cent and 1.6 per cent, respectively.
Airlines and cruise operators, among the hardest hit by the pandemic, also fell.
The S&P 1500 airlines index dropped 3.1 per cent, while Royal Caribbean Cruises Ltd fell 4 per cent and Carnival Corp tumbled almost 8 per cent.
"The market is reacting to the rise in COVID cases nationwide," said Michael Antonelli at Baird in Milwaukee.
"Vaccine news helps at some point in the future but today we are dealing with an accelerating spread,"
Even after Thursday's drop, the S&P 500 has gained almost 2 per cent this week, buoyed by positive vaccine trial data that increased expectations of quick recovery.
Stocks have also benefited from expectations a divided Congress will prevent president-elect Joe Biden enacting tax hikes that would hurt corporate profits.
"The reality is we don't know what the new normal is going to look like, even when we do recover from the coronavirus and that is still a ways away," said Tom Martin at Globalt Investments in Atlanta.
"It's the classic between the market discounting something that is nine to 12 months out and then 'undiscounting' it because it has not happened yet."
In extended trade, Cisco Systems Inc jumped 8.6 per cent after the network gear maker's quarterly results.
New data showed US jobless claims at a seven-month low last week but the pace of job recovery slowed as fiscal stimulus waned and further improvement could be limited by a raging pandemic.
Unofficially, the Dow Jones Industrial Average fell 1.08 per cent to end at 29,080.17 points, while the S&P 500 lost 1.00 per cent to 3,537.01.
The Nasdaq Composite dropped 0.65 per cent to 11,709.59.
Among the biggest boosts to the Nasdaq was a surge 20 per cent in the US-listed shares of Chinese e-commerce company Pinduoduo Inc after it reported strong quarterly revenue.
The S&P 500 energy index slumped 4 per cent and materials lost 2.5 per cent.
Moderna Inc rallied 6.5 per cent after the drugmaker said it had enough data for a first interim analysis of the late-stage trial of its experimental COVID-19 vaccine.
On US exchanges, 10.3 billion shares changed hands, compared to an average of 10.0 billion shares for the last 20 sessions.
Declining issues outnumbered advancing ones on the NYSE by a 2.95-to-1 ratio; on Nasdaq, a 2.17-to-1 ratio favoured decliners.
The S&P 500 posted five new 52-week highs and no new lows; the Nasdaq Composite recorded 70 new highs and 11 new lows.