Financials and other cyclical groups, which often outperform when the economic outlook improves, declined. Only two of the 11 major S&P sectors were positive, with tech leading.

Stocks have rebounded sharply since late March from the coronavirus-fueled sell-off, helped by massive monetary and fiscal stimulus.

"We are dealing with a very fragile rally," said Michael Purves, chief executive officer at Tallbacken Capital Advisors. "Selling into the close doesn't make you feel good."

The Dow Jones Industrial Average fell 218.45 points, or 0.91%, to 23,664.64, the S&P 500 lost 20.02 points, or 0.70%, to 2,848.42 and the Nasdaq Composite added 45.27 points, or 0.51%, to 8,854.39.

US private employers laid off a record 20.236 million workers in April as mandatory business closures in response to the novel coronavirus outbreak savaged the economy.

The Labor Department's more comprehensive report for April is due on Friday.

Investors are now watching efforts by a number of states to spark their economies by easing restrictions put in place to fight the outbreak.

In company news, General Motors Co jumped 3.0% after the automaker topped first-quarter profit expectations and outlined plans for a May 18 restart of most of its North American plants.

Occidental Petroleum Corp shares fell 12.5% after the company said it was looking to raise new cash or swap debt for stock, a day after it posted a large first-quarter loss.

Declining issues outnumbered advancing ones on the NYSE by a 2.31-to-1 ratio; on Nasdaq, a 1.42-to-1 ratio favored decliners.

The S&P 500 posted six new 52-week highs and two new lows; the Nasdaq Composite recorded 56 new highs and 23 new lows.

About 9.7 billion shares changed hands in US exchanges, compared with the 11.8 billion daily average over the last 20 sessions.