Amazon.com Inc said today it would buy US organic supermarket chain Whole Foods Market Inc for $13.7 billion, including debt, marking the internet retailer's largest deal and biggest foray into the brick-and-mortar retail sector.

The deal, which puts a 27 per cent premium on Whole Foods' closing share price on Thursday, would could give the grocer a major competitive edge by allowing it to tap into Amazon's massive power to buy and sell goods at a lower cost.

Whole Foods recently had come under pressure from activist hedge fund Jana Partners LLC, prompting it to overhaul its board.

"I think that this takes all of the pressure off Whole Foods and gives Whole Foods the opportunity to revitalise that business and of course it stems the criticism from all of these activist investors," said Neil Saunders, managing director of GlobalData Retail in New York.

Excluding debt, the deal is valued at $13.39 billion, based on 318.9 million diluted shares outstanding as of April 9.

The grocer would continue to operate stores under the Whole Foods Market brand, the companies said.

John Mackey will continue as chief executive of Whole Foods, and the company's headquarters will remain in Austin, Texas.

Amazon and Whole Foods expect to close the deal during the second half of 2017.