Amazon.com Inc said on Friday it would buy Whole Foods Market Inc for $13.7 billion, in an embrace of brick-and-mortar stores that could turn the high-end grocer into a mass-market merchant and upend the already struggling US retail industry.

Amazon used aggressive pricing to become an e-commerce retail juggernaut and has recently been experimenting with brick-and-mortar outlets. It will take over a natural and organic grocer pioneer with 456 stores, a mecca for young, high-end shoppers, that has been struggling to rein in prices and integrate technology.

The deal represents a dramatic turn in strategy for Amazon, which has offered food delivery through its Fresh service for a decade but has not made a major dent in the $700 billion grocery market.

“The ramifications for all of retail are seismic – not just retailers that sell grocery, but for everyone,” Gordon Haskett analyst Chuck Grom said.

Shares of dozens of supermarkets, food producers, payment processors and shopping malls collectively lost at least $35 billion in US market value on Friday as the news reverberated across financial markets.

Shares of grocer Kroger Co swooned 9.2 percent, while Wal-Mart Stores Inc fell 4.7 percent, signaling fears that Amazon could broaden Whole Foods' product mix and cut prices.

Amazon's shares rose 2.4 percent to $987.71, adding $11 billion to its market capitalization, which in one sense makes the acquisition nearly free for Amazon shareholders.

"Supermarkets will now have to contend with not only competition with each other and non-traditional grocers like Wal-Mart Stores Inc and Target Corp, but with a retailer like Amazon which has the financial capacity to price aggressively," said Mickey Chadha, vice president and senior credit officer at Moody's Investors Service.

Amazon agreed to pay $42 per share in cash for Whole Foods, a 27 percent premium on the Austin, Texas-based grocer's closing share price on Thursday.

But in a sign that investors believe a rival bid is likely, Whole Foods shares rose above the offer price to close at $42.68.