WASHINGTON — The International Monetary Fund issued a stark warning on Tuesday about the coronavirus’s economic toll, saying that the world is facing its worst downturn since the Great Depression as shuttered factories, quarantines and national lockdowns cause economic output to collapse.

The grim forecast underscored the magnitude of the shock that the pandemic has inflicted on both advanced and developing economies and the daunting task that policymakers face in containing the fallout. With countries already hoarding medical supplies and international travel curtailed, the I.M.F warned that the crisis threatened to reverse decades of gains from globalization.

In its World Economic Outlook, the I.M.F. projected that the global economy would contract by 3 percent in 2020, an extraordinary reversal from early this year, when the fund forecast that the world economy would outpace 2019 and grow by 3.3 percent. This year’s fall in output would be far more severe than the last recession, when the world economy contracted by less than 1 percent between 2008 and 2009.

“As countries implement necessary quarantines and social distancing practices to contain the pandemic, the world has been put in a Great […]