Bezos' fortune was $65.3 billion as of 4:30 p.m. EDT (2030 GMT) on Thursday, compared with Buffett's $64.9 billion.

Microsoft Corp (MSFT.O) co-founder Bill Gates remained the world's richest person, at $77.7 billion, while Spain's Amancio Ortega, who founded the Zara clothing chain's owner Inditex SA (ITX.MC), was second at $72.7 billion. Facebook Inc (FB.O) co-founder and chief executive Mark Zuckerberg was fifth, at $54 billion.

Bezos, 52, owns close to 18 percent of Amazon. Its stock has risen by roughly 50 percent since early February, as the world's largest online retailer continued to upend retailing as more people took to the Web rather than the mall to shop.

Amazon's share price rose further in after-hours trading, after the Seattle-based company reported better-than-expected second-quarter results.

Buffett, 85, owns close to 18 percent of Berkshire, but his donation this month of $2.86 billion of Berkshire stock to the Bill & Melinda Gates Foundation and four family charities led to his drop to fourth place. He has donated more than $24.3 billion to the Gates Foundation and family charities since 2006.

Berkshire is based in Omaha, Nebraska, and has roughly 90 business units including Geico car insurance, the BNSF railroad and Dairy Queen ice cream.

In June, Buffett called Bezos a "classic example" of how a business owner could thrive, by having focused at Amazon on how to "delight" customers, and keep them coming back, rather than simply process their orders.

(Reporting by Jonathan Stempel in New York; Editing by Alan Crosby)