WASHINGTON (AFP) -- American billionaire Warren Buffett has indicated that a successor to head his Berkshire Hathaway firm has already been "agreed on" and could step in as soon as the investment guru retires or dies.

"There's several people, but there's one person they've all agreed on," Buffett, speaking of his holding company's board of directors, said Monday on the PBS network show "Charlie Rose," according to a transcript.

Without naming names, the Berkshire founder and chairman known as the Oracle of Omaha said that "if I die tonight, tomorrow morning it won't take the board an hour to have announced my successor."

Last October Buffett hinted that Berkshire Hathaway's newly appointed investment manager Todd Combs could one day head investments for his massive company.

The 40-year-old Combs had been little known in the US business world, having spent the last five years running Castle Point Capital Management.

Questions about the octogenarian's successor also swirled in March, when Berkshire top executive David Sokol, who had also been tipped by some to replace Buffett at the helm of the $372 billion investment house, resigned after a share-buying scandal.

In the interview, Buffett also said he was "100 percent" opposed to the decision by ratings agency Standard & Poor's earlier this month to ding the United States' sterling AAA credit rating for the first time, a move which sent markets into a panic, although they stabilized in the days after the downgrade.

Buffett also warned on PBS of the "very, very stark statement" by the US Federal Reserve last week when it pledged to hold interest rates near zero for two more years to counter an economy facing increased risks of stalling.

"They're really saying the economy is not going to be very good until then," Buffett said. "There's a chance they're wrong."

Buffett earlier had pricked the ears of investors, politicians and analysts by writing an opinion piece in Monday's New York Times urging lawmakers to raise taxes on wealthier Americans, including the mega-rich like him, in order to cut the country's huge budget deficit, saying the move would not dampen investments or jobs.