Warren Buffett is keeping secret the identity of the person likely to succeed him as CEO of Berkshire Hathaway but he is narrowing the field - he says the top choice and two backups are men.

Buffett is getting questions about his successor because he is 81 years old and was recently diagnosed with prostate cancer although the disease is not expected to threaten his health.

Buffett has said Berkshire's board has chosen his successor, but doesn't want to name him because the choice could change.

Buffett said during an interview with Fox Business on Monday that he's not making any effort to teach his successor how to run Berkshire. He says none of his potential successors need to be treated like apprentices.

He expects his successor will maintain the company culture.