Amazon CEO Jeff Bezos briefly became the world's richest man Thursday in Forbes magazine's tracking of wealth, as stock in his e-commerce company hit an all-time high.

Microsoft founder Bill Gates reclaimed the lead by afternoon, as Amazon's stock fell nearly 1 per cent for the day to $1,046 US.

Amazon shares have been trading at a record high. They hit $1,083.31 US at about noon Thursday. According to securities filings, Bezos owns about 80 million shares, or 17 per cent; those shares were valued at more than $87 billion US at the peak. Bezos also owns The Washington Post through a holding company.

Forbes said Bezos' net worth was about $90.6 billion US when the market opened Thursday. Gates had $90.1 billion US. Forbes said Gates would have been the undisputed leader had he not given billions of dollars away to various philanthropic causes. Bezos issued a request for philanthropic ideas in a tweet in June, just before Amazon announced a $13.7 billion US deal for organic grocer Whole Foods.

The changes in Bezos' fortune coincided with Amazon's report of a 77 per cent decline in quarterly profit on heavy spending. Shares fell in after-markets trading as the company missed Wall Street's expectations on profit.