SAN FRANCISCO: Amazon, the online retail giant, has joined forces with the US Postal Service (USPS) to deliver groceries to the homes of its customers in San Francisco.

A USPS spokeswoman confirmed that the two companies began testing the home-delivery service in the first week of August and the trial is expected to last 60 days, Internet Retailer reported.

Using the AmazonFresh brand, which has operated in Amazon's home city of Seattle since 2007, deliveries of meat and other groceries are shipped in insulated bags to customers' doorsteps between 3am and 7am in the morning.

Most USPS trucks are not operational during the early hours and the use of insulated bags means deliveries can be made without having to use refrigerated transport.

The test will "determine if delivering groceries to residential and business addresses would be feasible from an operations standpoint and could be financially beneficial," USPS said.

Amazon already uses USPS for its Sunday delivery service, which it launched last November in New York and Los Angeles, and it has since expanded to Columbus in Ohio, Waco in Texas, and 13 other cities.

"We were already working closely with Amazon – it's been a good relationship – and conducting this test is expanding on that existing relationship," said the USPS spokeswoman.

If successful, the relationship could prove beneficial for both parties, the Wall Street Journal reported, because Amazon is seeking to expand its Fresh service beyond Seattle, Los Angeles and San Francisco, while the extra income would be welcome for the loss-making USPS.

Customers of AmazonFresh receive free delivery for purchases of more than $35, as long as they pay a $299 annual membership fee, while non-members are charged between $7.99 and $9.99 on deliveries of less than $100, after which it is free.

Data sourced from Internet Retailer, Wall Street Journal; additional content by Warc staff