Prices of U.S. Treasury securities rose as the Bank of Japan conducted emergency operations and stocks in the nation slumped, following the nation’s biggest earthquake on record last week.

Two-year yields approached the lowest level in five weeks as investors sought the safest securities. The TED spread, the difference between what banks and the U.S. government pay to borrow for three months, widened to 24 basis points, the most since August.

“Investors are in a flight to quality,” said Hiroki Shimazu, an economist in Tokyo at Nikko Cordial Securities Inc., a unit of Sumitomo Mitsui Financial Group Inc., Japan’s third- largest publicly traded bank by assets.

The yield on the 10-year note fell two basis points to 3.39 percent as of 9:17 a.m. in Tokyo, according to data compiled by Bloomberg. The 3.625 percent security due February 2021 gained 1/8, or $1.25 per $1,000 face amount, to 101 31/32.

The two-year rate slipped four basis points to 0.61 percent.