Treasury bond yields are plunging to levels seen in the 1950s on concern the two-year recovery in the world's largest economy is stalling.

Yields on benchmark 10-year U.S. notes are about 4.3 percentage points below the average over the past 49 years and almost where they were when President Dwight D. Eisenhower began his administration in 1953. The yield, which dropped to 2.40 percent today in New York, reached a record low of 2.04 percent in December 2008 during the global financial crisis.

Investors are piling into Treasuries after the European Central Bank resumed bond purchases and made more cash available to banks to keep the region's debt crisis from spreading and the Japanese and Swiss central banks sought to protect their economies against declines in the dollar and euro. The Standard & Poor's 500 Index had its biggest drop since 2009 and markets worldwide have tumbled since a July 29 report showing gross domestic product climbed less than an earlier estimate in the second quarter renewed speculation the Federal Reserve will have to resort to more stimulus measures to avert another recession.