Stocks fall again as stimulus firepower fails to impress Wall Street

US stock futures swung back into the red overnight after Wall Street's slight rebound. Dow futures fell more than 800 points, or 3.9%, accelerating earlier losses after hours. S&P 500 futures were down 3.7%, while Nasdaq futures declined 4.4%. Markets in Asia and Europe also fell again.

The US administration and European governments are promising trillions of dollars in support for their economies as they try to prevent the virus from putting millions of people out of work and bankrupting industry.

US Treasury Secretary Steven Mnuchin is pushing for a $1 trillion economic stimulus designed to prevent the unemployment rate from soaring to 20%, a Republican Senate source told CNN. Germany, France, Spain and the United Kingdom have also pledged more than $1.5 trillion combined in business loans and other support.

"Volatility across markets has created considerable anxiety amongst investors trying to gauge the effectiveness" of various healthcare, monetary and fiscal policy responses, wrote Bob Michele, global head of fixed Income at JP Morgan Asset Management, in a research note.

The US market jitters carried over to Asia Pacific during Wednesday trade.

Australia's S&P/ASX 200 closed down 6.4%, the worst performer in the region. South Korea's Kospi ended the day down 4.9%.

Other major regional indexes turned negative, erasing morning gains. Japan's Nikkei 225 finished down 1.7%, China's Shanghai Composite was last down 1.8% and Hong Kong's Hang Seng Index was 4.2% lower as its losses accelerated rapidly toward the end of the day.

Europe's STOXX 600 index was down 3.3% in early trading, while Germany's DAX was off 4.6% and France's CAC 40 has slid 3.6%. Britain's FTSE 100 was 3.3% lower.

Fears about the financial and economic impacts of coronavirus have spurred massive swings in the markets in recent weeks.

The Dow finished Tuesday up more than 1,000 points, or 5%. The S&P 500 and Nasdaq both closed up around 6%.

Wall Street was buoyed by continued action by the New York Federal Reserve to calm the panicked financial markets. The NY Fed announced Tuesday it will conduct two $500 billion overnight operations each day this week.

The overnight lending markets provide critical funding to banks, hedge funds and other financial institutions — markets that came under pressure last fall and have again been strained in recent days as recession fears rise.

The Fed also announced plans Tuesday to unfreeze the $1 trillion commercial paper market. That should help businesses get short-term loans to pay workers and finance inventories.

— Matt Egan contributed to this report.