The Dow Jones Industrial Average dropped nearly 3,000 points Monday—its steepest decline of the monthlong selloff—reflecting fear the emergency measures taken by the Federal Reserve may not be enough to ward off a coronavirus-induced recession.

The decline underscores the level of worry among investors since the coronavirus pandemic escalated and disrupted supply chains, sidelined workers and infected tens of thousands of people. To combat the potential economic fallout, central banks and governments have put in place various...