The Dow fell nearly 800 points Tuesday and 10-year Treasury yields dipped below 1% for the first time ever in a day of wild swings triggered by a surprise Federal Reserve rate cut and the latest news of the coronavirus’s spread.

After the Fed lowered its key interest rate by half a percentage point earlier in the day, the Dow Jones industrial average surged more than 400 points before tumbling as much as 900 points. The rate cut was aimed at supporting the economy and financial markets but may have had the opposite effect, analysts say.

“It was perhaps a sign the Fed is concerned about the economy,” says Ryan Detrick, senior market strategist for LPL Financial. “Maybe things are a little worse than we thought.”

The central bank may have been better off trimming rates by just a quarter percentage point and then cutting by another quarter-point at its March 17-18 meeting, says Nick Reece, senior analyst at Merk Investments.

Reece also believes markets were responding to news that problems with test kits prevented some states from testing for the disease. Also, officials confirmed a seventh death in the U.S. from the outbreak.

The Dow Jones industrial average ended the day down 786 points, or 2.9%, at 25,917. The broader Standard & Poor's 500 index fell 87 points, or 2.8%, to 3003.37. The Nasdaq slid 1.3%.

The 10-year Treasury yield fell to 0.993% -- a sign that investors foresee slow economic growth and inflation ahead, Reece says. Detrick, though, says it largely signifies that global investors are buying safe assets like Treasurys when uncertainty is more pronounced In Europe and Asia.

The Fed has a long history of coming to the market's rescue with lower rates and other stimulus, which has helped this bull market in U.S. stocks become the longest in history. Some analysts said the Fed's latest cut should provide some more confidence.

“Confidence in markets is crucial,” said Quincy Krosby, chief market strategist at Prudential Financial. “Without confidence, you don’t have a market.”

The Dow had jumped 5% Monday to its best day in more than a decade on rising anticipation for aid from the Fed and other central banks. Even before Tuesday's rate announcement, traders were convinced that the Fed would cut rates by half a percentage point at its next meeting, scheduled for March 17-18. Monday's surge followed up the worst week for the S&P 500 since the financial crisis as worries about the virus' economic toll mounted.

But doubts are high about whether the medicine provided by central banks can be as effective this time around. Lower rates can encourage shoppers and businesses to borrow and spend more, but they can't reopen factories that have been shut or recall workers out due to quarantines.

Fed Chairman Jerome Powell said the central bank recognizes the fast spread of the virus is a risk for the economy, and he cited concerns from the travel and hotel industries. The high stakes pushed the Fed to cut rates outside of a regularly scheduled meeting for the first time since the 2008 financial crisis, when investors were considering a complete meltdown of the world's financial system as possible if not likely. That in itself may have added to the market's dread Tuesday.

“I don’t believe that market participants woke up this morning thinking we were facing a crisis similar to the global financial crisis," said Kristina Hooper, chief global market strategist at Invesco. "But that’s what the Fed’s actions suggested to some.”

She said investors will likely have mixed emotions about the move for days.

A gauge of fear in the stock market swung wildly up and down through the day. The VIX measures how much traders are paying to protect themselves from future swings in stocks, and it was relatively flat in early afternoon trading at 33.40. But it had eased as low as 25 immediately after the Fed's announcement, only to swing up to 35 an hour and a half later.

Earlier in the day, the Group of Seven major industrialized countries pledged support for the global economy, but they stopped short of announcing any specific new measures. Disappointment in the lack of action helped push U.S. stocks lower at the opening of trading, before the Fed surprised markets with its announcement of the steep, half-point rate cut at 10 a.m. Eastern time.

The G-7, which includes the U.S., Japan and Germany, among others, made its statement after weeks of warnings from companies that the virus will hit their finances. Economic groups have also warned of worsening forecasts for global economic growth.

Investors are still speculating whether other central banks will join and cut rates and offer stimulus in a coordinated effort around the world. Before the Fed made its move, the Reserve Bank of Australia cut its key interest rate to a record low 0.5%.

Payments processor Visa is among the latest companies warning investors. It expects first-quarter revenue to suffer because of the damage to international travel. Chipmaker Microchip Technology withdrew its profit forecast for the year because of the uncertainty surrounding the virus’ impact.

Worldwide, more than 90,000 people have been sickened and 3,100 have died. The number of countries hit by the virus has reached at least 70, with Ukraine and Morocco reporting their first cases.

U.S. markets have been hit hard by fear over the virus’ impact. Stocks surged on Monday over hopes that central banks will help shield the global economy. That followed a broad sell-off last week that erased gains for 2020 and sent indexes into what market watchers call a "correction," or a fall of 10% or more from a peak.

AP Business Writers Stan Choe and Damian J. Troise contributed to this report.