NEW YORK (Bloomberg) - Bear Stearns Cos. shares rose the most in five weeks on speculation that investors including Warren Buffett may buy all or part of the company.

Bear Stearns gained $12.16, or 11 percent, to $126.40 as of 3.28pm in New York after the New York Times said Buffett and others are negotiating to buy as much as 20 percent of the fifth-largest US investment bank.

The negotiations with Buffett, chief executive officer of Berkshire Hathaway Inc., and the other are "serious," The Times said, citing unidentified people familiar with the matter.

"It's a good thing any time Warren Buffett buys a piece of a company or is thinking of it," said Joseph Saluzzi, co-head of equity trading at Themis Trading LLC in Chatham, New Jersey. "You can't go wrong with a guy like that behind you."

Berkshire spokeswoman Jackie Wilson said nobody was available to comment. Bear Stearns spokesman Russell Sherman declined to comment.

Bear Stearns stock has fallen 22 percent this year on concern losses in mortgage-backed bonds will slow its profit growth.

The stock advanced earlier today on speculation "that a Chinese bank is looking to take a significant stake," said Marc Weinberger, head trader at W. Quillen Securities in New York.

Bear Stearns held negotiations in 2006 about selling a stake to China Construction Bank Corp., the nation's second-biggest bank, the Wall Street Journal reported this month. The negotations broke down when China Construction's president left the bank.

In June, two hedge funds managed by Bear Stearns collapsed because of bad bets on sub-prime mortgages. The losses helped trigger a month-long rout in credit and stock markets worldwide.

Some investors have bought Bear Stearns shares since then, betting on a rebound. Billionaire Joseph Lewis became the firm's largest holder, paying $860.4 million for a seven percent stake, according to a September 10 filing with the US Securities and Exchange Commission.