The yield on the 30-year US Treasury bond plummeted to an all-time low Wednesday as investors seized on safe assets following a weak US retail sales report.
Near 1720 GMT, the yield on the 30-year bond stood at 2.41 percent, down from 2.50 percent Tuesday after earlier falling to a record low of 2.39 percent.
The yield on the 10-year bond sank to 1.82 percent from 1.90 percent, hitting its lowest level since May 2013. Bond prices and yields move inversely.
"It's really concerns about global economic growth which is driving a lot of money into the US Treasury market and driving down those yields," said Paul Edelstein, director of financial economics for IHS Global Insight.
The push into treasuries came as US stocks headed for a fourth straight day of losses, with the Dow Jones Industrial Average off about 1.5 percent.
Oil prices lingered near six-year lows and prices of copper, another commodity closely associated with global growth, slumped to a six-year low. European equities were also down sharply.
The volatility came after US retail sales for the key December period declined a steep 0.9 percent, spurring worries about the US economic recovery.
Investors still think the US economy will do well in the next couple of years. But the surge in bond buying reflects a gloomier long-term economic outlook, Edelstein said.
Factors driving this shift, he said, include stagnation in Europe and other regions, concerns that future technological advances will not be as great as in the recent past, worries that growth is ebbing from peak levels in China and other economies and unfavorable demographic trends in the US and Europe.
"It's a lot of issues," Edelstein said.
"There is some expectation over, not necessarily the next five years, but maybe beyond that, that rates are going to be lower than we're used to because inflation and growth are going to be weak."