Amazon is considering opening up to 3,000 new cashier-less stores by 2021 to vie for shoppers at convenience stores and quick-service sandwich shops, Bloomberg News reported .CEO Jeff Bezos is trying to decide on the best format for this bold and expensive venture, Bloomberg said, quoting people familiar with the matter.

The new AmazonGo outlets could be convenience stores offering fresh prepared foods and some groceries, like 7-Eleven, or just a place to grab a quick bite to eat, one of the sources told Bloomberg. The company unveiled its first cashier less store near its headquarters in Seattle in 2016.

Since then it has announced two additional sites in Seattle and one in Chicago, Bloomberg said.It said shoppers use a smartphone app to enter the store and once they scan their phones at a turnstile, can choose from a range of salads, sandwiches, drinks and snacks. Then they leave without stopping at a cash register.

The Amazon Go store, which has no cashiers and allows shoppers to buy things with the help of a smartphone app, is widely seen as a concept that can alter brick-and-mortar retail.

Customers have to scan a smartphone app to enter the store. Once inside, cameras and sensors track what they pick up from the shelves and what they put back. Amazon then bills shoppers’ credit cards on file after they leave.

Sensors and computer-vision technology detect what shoppers take and bill them automatically, Bloomberg said.