SEATTLE — Amazon.com Inc. continues to experiment with physical stores to supplement its extensive online retailing ­presence.

The e-tailer last month opened two Seattle grocery pickup sites — previously being “beta tested” and accessible only to Amazon employees — to the public. Amazon Prime members can now buy groceries online and opt to pick them up at drive-in facilities in the neighborhoods of Ballard and Sodo. Called AmazonFresh Pickup, the locations, with groceries brought to shoppers’ cars, are the latest example of the e-commerce giant’s attempt to make inroads against traditional retailers.

Walmart, meanwhile, has been battling Amazon on the e-commerce front, most recently with discounts for consumers who order certain online-only items and pick them up at a store instead of having them delivered to their homes. The launch follows Walmart’s acquisition of niche e-tailers Jet.com Inc., ShoeBuy, Moosejaw and ModCloth.

Amazon’s brick-and-mortar openings are part of an attempt to encroach on supermarket sales that has included its decade-long offering of the AmazonFresh grocery deliver service. The $14.99-a-month service has failed to make a significant dent in the businesses of supermarket chains and Walmart Supercenters.

Besides the new grocery pickup sites, Amazon has been operating a cashierless convenience store in Seattle, called Amazon Go. It was expected to open to the public early this year, but has been available only to employees, reportedly because of kinks in the technology.

And last month brought the premiere, in New York City, of the company’s seventh brick-and-mortar book store. The Amazon Books outlet, located at Columbus Circle in Manhattan, joins outlets in Chicago; Portland, Ore.; San Diego; Seattle; and Dedham and Lynfield, Mass. Amazon plans to open six more book stores this year.

The outlets take a technology-oriented approach, with scanners and apps that let shoppers find out more about the books that interest them, and pay for their purchases with the Amazon app on their smartphones.