A day after Warren Buffett's Berkshire Hathaway Inc lost its triple-A credit rating, its shares rose to the highest since mid-January after Wells Fargo & Co , one of its largest investments, projected a surprise $3 billion first-quarter profit.

Berkshire's Class A shares were up $2,330, or 2.6 percent, at $91,290 in afternoon trading after earlier rising to $92,880, their highest since January 16, Reuters data show.

Wells Fargo said on Thursday it expects quarterly profit excluding preferred stock dividends of 55 cents per share, more than twice what analysts expected.

The San Francisco-based bank said it benefited from a surge in mortgage lending, lower credit losses than analysts feared, and strong results from newly-acquired Wachovia Corp.

As of December 31, Berkshire said it held 304.4 million Wells Fargo shares, for a 7.2 percent stake.

Wells Fargo shares rose as much as 32.6 percent on Thursday, which would give Omaha, Nebraska-based Berkshire an instant paper profit from that stake of close to $1.5 billion.

Berkshire also holds large stakes in other U.S. financial companies, including American Express Co and U.S. Bancorp , whose shares also had strong gains.

On Wednesday, Moody's Investors Service lowered Berkshire's credit rating two notches to Aa2 from Aaa and also cut several other ratings. It cited the impact of the recession on Berkshire's nearly 80 operating businesses and of falling stock prices on Berkshire's investments.

The lower ratings nevertheless remain very high and are not likely to meaningfully affect Berkshire's operations.

Berkshire owns a roughly 20 percent stake in the rating agency's parent, Moody's Corp , but has said it does not exercise control over the ratings.

Fitch Ratings in March took away its equivalent AAA rating from Berkshire, but that rating agency it is smaller and less widely followed than Moody's. Standard & Poor's has said it might downgrade Berkshire with a year.

Buffett is the world's second-richest person, trailing Microsoft Corp co-founder and Berkshire director Bill Gates, according to Forbes magazine.

(Reporting by Jonathan Stempel; Editing by Andre Grenon)