The Dow Jones Industrial Average of 30 major American companies fell more than 4.5% on Friday, erasing all the gains it had made since Donald Trump became president in January 2017.
The drop helped to finish the worst week on Wall Street since 2008, with all three indexes down at least 12%.
The falls come as authorities tighten restrictions on activity in an effort to slow the spread of the coronavirus.
New York state on Friday ordered non-essential businesses to close.
Illinois also made a similar move, while California earlier mandated that its residents shelter in place.
The Dow lost more than 900 points to close at 19,173, while the wider S&P 500 dropped 4.3% to 2,304 and the Nasdaq lost 3.8% to 6,879.5.
They have now fallen more than 30% from their recent records.
Mr Trump has taken credit as the share indexes climbed during his presidency – gaining nearly 50% as of last month. He has written about them on Twitter at least 131 times, according to a tally by the New York Times.
At briefings this week, Mr Trump has said he is not worried about the economy in the long-run, arguing that business will bounce back after the pandemic eases and restrictions can be relaxed.
For now, however, the upheavals are severe.
Unemployment claims in the US surged 30% this week, as thousands of people lost their jobs, while in the restaurant industry alone as many as 7 million jobs could be cut in the next three months, according to estimates by the National Restaurant Association.
Delta Air Lines on Friday said it would lose $10bn in its second quarter, while United Airlines warned that it would cut jobs starting in April if the government does not provide relief funding. Both firms saw share prices fall about 30% this week.
Coca-Cola lost more than 8%, after warning the virus had upended its growth forecast, as sales to theatres, sporting venues and restaurants evaporate.
Earlier, the FTSE 100 index of top UK firms ended up 0.76%, while Germany’s Dax and France’s CAC 40 gained more than 3%.
Source: BBC News