NEW YORK — Fear and uncertainty continue to control Wall Street, and stocks fell sharply Tuesday after an emergency interest-rate cut by the Federal Reserve failed to reassure markets wracked by worries that a fast-spreading virus will cause a recession.

The Dow Jones Industrial average sank 785 points, or 2.9 percent. It had surged 5 percent a day earlier on hopes for a broader set of stimulus measures.

While the cut gave some investors exactly what they had been asking for, Federal Reserve Chairman Jerome Powell acknowledged that the ultimate solution to the virus challenge will have to come from health experts and others, not central banks. Some traders are also questioning whether more aid is on the way to stabilize the market, while others called the Fed’s move premature to begin with. For more than a few, the Fed’s steepest rate cut since 2008 recalled the dark days of the financial crisis and only added to the dread.

Through it all, markets are still faced with the same quandary that has sent stock prices tumbling 11 percent since they set a record just two weeks ago: No one knows how far the virus will ultimately spread before authorities can get it under control, and by how much companies’ profits will be shorn because of it.

That uncertainty led to jagged trading across markets on Tuesday. Stocks rallied briefly in the morning following the Fed’s surprise move, but it took just 15 minutes for the gains to evaporate. The yield on the 10-year Treasury fell below 1 percent for the first time in history as investors ratcheted back expectations for the economy and inflation. A gauge measuring traders’ fear of upcoming swings for stocks jerked wildly up and down through the day.

After popping to a 1.5 percent gain shortly after the Fed’s announcement, the S&P 500 swung between modest gains and losses for about an hour before turning decisively lower. The index ended the day down 86.86 points, or 2.8 percent, at 3,003.37. It pared a loss that reached 3.7 percent in the mid-afternoon, and it marks the eighth drop in the last nine days for the index.

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 on record. Some analysts said the Fed’s latest cut could 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 Jones Industrial Average had jumped 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 announcement, traders were convinced that the Fed would cut rates by half a percentage point on March 18 at its next meeting.

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.

After the Fed’s announcement, Powell acknowledged that central banks can’t solve the health crisis. But he said the Fed recognizes the fast spread of the virus is a risk for the economy, and he cited concerns from the travel and hotel industries. Powell said that since last week, when several Fed officials had said they saw no urgent need to cut rates, “we have seen a broader spread of the virus.”

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 spooked the market, as some investors wondered if the Fed saw things as worse than they were led to believe.

“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.

Some economists called the Fed’s move premature, given that U.S. economic data has yet to show a sharp drop due to the virus.

“The nature of today’s announcement could send the wrong signal to market participants, including individual investors who are concerned with recent market volatility,” said Roger Aliaga-Diaz, chief economist of the Americas at Vanguard.

Markets are likely to remain shaky until investors get a sense of what the worst-case scenario really is in this virus outbreak. Markets have been on edge for nearly two weeks, as the virus spreads beyond China and companies across continents and industries say they expect it to hit their profits.

Payments processor Visa on Tuesday joined the lengthening list of companies warning investors. It said its quarterly revenue will be weaker than earlier predicted because of a drop-off in travel-related spending on cards.

“To get a floor on the markets, realistically, what we need to see is not so much a cut in the number of new coronavirus cases, but at least a slowdown in the acceleration,” said Salvatore Bruno, chief investment officer for IndexIQ. “Up until that time, we’re likely to see a lot of volatility.”

Worldwide, more than 92,000 people have been sickened, and over 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.

The topsy-turvy Tuesday got off to a slow trading start in the United States. 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.

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 percent.

U.S. markets have been hit hard by fear over the virus’ impact. Monday’s surge for stocks on hopes that central banks will come to the rescue 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 percent or more from a peak. Last week was the worst for the S&P 500 since the financial crisis.

MARKET ROUNDUP:

The S&P 500 fell 86.86 points, or 2.8 percent, at 3,003.37. The Dow Jones Industrial Average lost 785.91 points, or 2.9 percent, to 25,917.41, and the Nasdaq fell 268.07, or 3 percent, to 8,684.09.

European stock markets were broadly higher, with the German DAX returning 1.1 percent, the French CAC 40 up 1.1 percent and the FTSE 100 up 1 percent. In Asia, Japan’s Nikkei 225 fell 1.2 percent, South Korea’s Kospi rose 0.6 percent, and stocks in Shanghai added 0.7 percent.

Bond yields swung following the Fed’s announcement. The yield on the 10-year Treasury slumped to 1.01 percent from 1.08 percent late Monday after earlier dropping below the 1 percent threshold for the first time. The 10-year yield tends to fall when expectations are for weak economic growth and inflation. Shorter-term yields, which move more on Fed actions, had even more dramatic drops. The two-year Treasury yield sank to 0.71 percent from 0.81 percent.