US billionaire Warren Buffett has donated $US1.25 billion ($A1.58 billion) in Berkshire Hathaway Inc stock to the Bill & Melinda Gates Foundation.

The gift is the third instalment in Buffett's plan to transfer the majority of his wealth to the Seattle-based foundation run by the Microsoft Corp chairman and his wife.

The foundation is the world's biggest with an endowment of $US27.5 billion ($A34.77 billion) as of April 2009.

Last year, before the recession depressed Berkshire Hathaway's stock, Buffett's gift of a similar number of shares was worth $US1.8 billion ($A2.28 billion), or 30 per cent more.

Thursday's filing with the Securities and Exchange Commission also lists donations of shares of Class B stock worth $US125 million ($A158.07 million) to the Susan Thompson Buffett Foundation and nearly $US50 million ($A63.23 million) each to the Sherwood Foundation, the Howard G Buffett Foundation and the NoVo Foundation.

Class B shares were worth $US2,924 ($A3,697) at the close of trading July 1, the day Buffett transferred their ownership.

Omaha, Nebraska-based Berkshire Hathaway owns a mix of more than 60 companies, including insurance, furniture, carpet, jewellery, restaurants and utility businesses.

AP