Investors were likely hopeful that USA lawmakers were close to settling on a stimulus bill meant to help the economy amid the coronavirus outbreak.
The S&P 500 has lost more than $9 trillion in value from its mid February record high, while the Dow Jones erased over three years of gains in one month.
Many traders have "reverted to the 2008 case study", when markets saw several 5% rallies during the global financial crisis before bottoming out in March 2009, Chris Weston of Pepperstone said in a report.
The stimulus includes a $500 billion fund to help hard-hit industries and a comparable amount for direct payments of up to $3,000 apiece to millions of USA families. Overall, more than 111,000 have recovered. For some, especially older adults and people with existing health problems, it can cause more severe illness, including pneumonia and death.
The choppy trading came after the Dow surged more than 2,100 points on Tuesday on hopes that Congress would finally match the Federal Reserve's aggressive response to the coronavirus.
Wall Street had another rare positive session on Wednesday, with key indices posting their second consecutive day of gains amid expectations government stimulus to fight the coronavirus outbreak is coming soon.
At the close, Dow +2.4% and S&P 500 +1.1%, but the Nasdaq ended slightly in the red, -0.4%.
"People have to contend with the idea that the longer that lasts, the more people potentially are losing their job", said Yousef Abbasi, director of USA institutional equities at INTL FCStone.
"The secretary stressed that as a leader of the G20 and an important energy leader, Saudi Arabia has a real opportunity to rise to the occasion and reassure global energy and financial markets when the world faces serious economic uncertainty", she said.
The S&P 500 was down 1.4%, as of 10 a.m.
The Nasdaq fell 33.56 points, or 0.5%, to 7,384.30. The Russell 2000 index of smaller company stocks gained 13.79 points, or 1.3%, to 1,110.34. Boeing shares rallied 24% to lead the Dow higher. Other travel-related stocks also stormed higher to recoup a fraction of their huge losses over the last month.
American Airlines AAL.O , Royal Caribbean Cruises RCL.N and Norwegian Cruise Line Holdings NCLH.N , among the hardest hit by the coronavirus pandemic, jumped between 15% and 21%. It also said sales are bouncing back in China, where the outbreak has eased and most Nike stores have reopened.
European markets initially jumped to strong gains, but they faded as the day progressed. Germany's DAX was down 0.8%, and the French CAC 40 was up the same amount.
The planemaker has lost more than two-thirds of its value so far this year as the health crisis crimped travel demand, forcing it to seek $60 billion in USA government loans for the aerospace industry.