WASHINGTON—U.S. officials warned that much more needs to be done to slow the spread of the coronavirus and help the economy cope, urging Americans to significantly curb their social activity and calling for more action from Congress.

On Sunday evening the Centers for Disease Control and Prevention recommended that gatherings of more than 50 people be canceled or postponed for the next eight weeks, including weddings, conferences and festivals.

The warnings Sunday came as the Federal Reserve slashed its benchmark interest rate to near zero, part of a bid to battle market disruptions.

The move was welcomed by the Trump administration, which has expanded restrictions on travel from Europe and faced criticism for how it was processing frazzled travelers who were struggling to return home from overseas. The administration also sought to expand access to tests for the virus, as the White House said over the weekend that President Trump himself had tested negative for coronavirus.

The federal government’s leading voice on infectious diseases said Americans—particularly younger people—must help prevent community spread of the virus, urging them to stay home and avoid unnecessary public outings.