By Jonathan Stempel and Jennifer Ablan

OMAHA, Nebraska (Reuters) - Warren Buffett's company Berkshire Hathaway Inc on Friday said first-quarter profit rose nearly 51 percent, helped by improved results in insurance and gains from its investments and derivative contracts.

Results topped expectations, and were released after Berkshire shares earlier in the day closed at a record high. On Saturday, Buffett and Berkshire Vice Chairman Charlie Munger will field shareholder questions at the company's annual meeting in its hometown of Omaha, Nebraska.

Net income increased to $4.89 billion, or $2,977 per Class A share, from $3.25 billion, or $1,966 per share, a year earlier.

Quarterly operating profit rose 42 percent to $3.78 billion, or $2,302 per share, from $2.67 billion, or $1,615 per share.

Analysts on average expected profit of $1,996 per share, according to Thomson Reuters I/B/E/S.

Book value per share, Buffett's preferred measure of growth, increased 5.5 percent from year end to $120,525 per Class A share, and Berkshire's cash stake grew over that period to $49.09 billion from $46.99 billion.

About $12 billion of cash is being used to fund a purchase by Berkshire and Brazil's 3G Capital of ketchup maker H.J. Heinz Co.

Revenue rose 15 percent from a year ago to $43.87 billion.

Operating profit from insurance operations, including the Geico car insurance and General Re reinsurance businesses, doubled to $1.7 billion from $845 million.

Nearly all of the improvement came from underwriting, where profit rose to $901 million from $54 million, in part because of a $255 million pre-tax gain in its reinsurance business.

Meanwhile, operating profit from noninsurance business rose 12 percent to $2.25 billion from $2 billion.

Berkshire owns more than 80 business units that sell such things as athletic apparel, chemicals, furniture and ice cream.

It also owns tens of billions of dollars of common stocks such as Coca-Cola Co, International Business Machines Corp and Wells Fargo & Co.

In Friday trading, Berkshire Class A shares closed up $1,993, or 1.2 percent, at $162,850. Its Class B shares closed up $1.34, or 1.2 percent, at $108.64.

(Reporting by Jonathan Stempel and Jennifer Ablan in Omaha, Nebraska; Editing by Bob Burgdorfer)