SAN FRANCISCO -- Google (GOOG) launched a same-day delivery service in the Bay Area on Thursday as the world's largest Internet search company works with retailers such as Target to compete more with e-commerce leader Amazon.com.

Google has been testing the service, called Google Shopping Express, with employees for a few months. The company opened it up to the public on Thursday morning in a limited launch focused on San Francisco residents and others living south of the city from San Mateo to San Jose.

Shoppers who sign up will get six months of free, same-day delivery of online orders placed with select retailers in the area. Google plans to charge for the service in the future, but it has not decided how much yet.

Companies taking part in the test include national retailers such as Target, Office Depot, Staples and Toys 'R' Us, and smaller, local firms such as Blue Bottle Coffee and Palo Alto Toy & Sport.

Google is working with local courier companies that pick up products from local stores and deliver them to shoppers' homes.

Google Shopping Express is the latest sign the company is expanding from its online search roots into e-commerce, where it is competing more with Amazon, the world's largest Internet retailer.

By getting into local delivery services, Google is joining an increasingly crowded field.

Walmart, the world's largest retailer, is testing a same-day delivery service called Walmart To Go in five metro areas.

EBay (EBAY) launched a same-day delivery service in San Francisco and New York last year.