Investors can't seem to get enough of U.S. government bonds.

A day after a record-setting auction of 10-year notes, the U.S. Treasury sold $13 billion of 30-year bonds Thursday at a record low yield of 2.58 percent. The previous low of 2.72 percent was set at the June auction.

The huge demand for low-yielding but ultrasafe Treasury securities is testament to investors' concerns over uncertainties in the global economy. Investors worry that Europe won't be able to contain its government debt crisis, China's economic growth will sputter and the U.S. won't resolve a budget crunch looming at the end of this year.

There were $2.70 in bids for every $1 worth of notes on sale, well above the average of $2.62 in the past four auctions.

The yield on benchmark 10-year note was 1.48 percent in late trading Thursday, down from 1.52 percent late Wednesday. The price rose 34.4 cents for every $100 invested.

The yield on 30-year bonds already in circulation fell to 2.56 percent from 2.62 percent late Wednesday. The bond's price rose $1.03 per $100.

The two-year note's yield fell to 0.25 percent from 0.27 percent. The three-month T-bill paid a yield of 0.10 percent, up from 0.09 percent.