WASHINGTON — In a surprise move, the Federal Reserve cut its benchmark interest rate by a sizable half-percentage point Tuesday in an effort to support the economy in the face of the spreading coronavirus.

Chairman Jerome Powell said at a news conference that the virus “will surely weigh on economic activity both here and abroad for some time.”

It was the Fed’s first move since last year, when it reduced its key short-term rate three times. It’s also the first time it has cut rates between policy meetings since the 2008 financial crisis, and it is the largest rate cut since then.

The Dow Jones Industrial Average, which had been down as much as 356 points shortly before the Fed’s announcement, initially jumped on the news.

The surge was short-lived. By mid-afternoon, the Dow had tumbled more than 700 points in a sign of nagging worries about economic damage from the virus.

Still, on Monday, the Dow had rocketed up nearly 1,300 points — its largest percentage gain since 2009.

The yield on the 10-year Treasury note fell below 1 percent for the first time ever. Investors around the world bid up bond prices — which move in the opposite direction of yields — as they sought safety from the stock market’s turmoil.

The fear that coursed through financial markets after the Fed’s announcement underscored the worry that there are limitations to what the Fed can do to resolve a crisis of this kind. Powell acknowledged as much when he observed that the “ultimate solution to this challenge will come from others, most notably health professionals.”