NEW YORK (Bloomberg) — The world's biggest bond investors can't stop buying Treasuries even though they're comparing government debt to Internet stocks just before the technology bubble burst.

The worst economy since World War II, credit-market losses exceeding $1 trillion and the biggest drop in the Standard & Poor's 500 Index since 1931 are luring investors to US debt just as the government prepares to sell a record amount to pay for the swelling budget deficit. Investors loaned money to the Treasury at zero percent interest this month to safeguard their principal from wider losses.

The Treasury sold $30 billion of four-week bills on December 9 at a rate of zero percent, the same day three-month bill rates turned negative for the first time since the US began selling the debt in 1929. Yields on two-, ten- and 30-year securities are below three percent. As recently as June the so-called long bond yielded 4.81 percent.

The drop in yields pushed returns on Treasuries to ten percent since October, led by a 37.5 percent gain in 30-year bonds.