The U.S. government's takeover of mortgage finance giants Fannie Mae and Freddie Mac may ultimately avert a "financial tsunami" in markets, the manager of the world's biggest bond fund said on Monday.

"I think this is the beginning of the end of the potential financial tsunami I talked about," said Bill Gross, chief investment officer of Pacific Investment Management Co, or Pimco, talking on CNBC television.

On Thursday, Gross wrote in his September Investment Outlook that to avoid systematic debt liquidation and halt a "financial tsunami", the U.S. government should give the Treasury the right to buy debt and other assets.

Gross said on CNBC on Monday that he would suggest that the initial costs of supporting Fannie and Freddie might be about $50 billion, but added that these costs are dependent on house prices and no one can be sure how much these will fall.

Asked what assets he was buying, Gross said on CNBC that mortgage securities "are attractive" because the Treasury has signaled that it will buy them in the future. "We want to buy them now" and sell them to the Treasury later, Gross said.