MOUNTAIN VIEW, United States — Google Inc. expanded its online shopping and delivery services to more U.S. cities as it challenges Amazon.com Inc. to win customers.

Chicago, Boston and Washington D.C. have been added to the Google Express service with more than 7 million people able to access its same-day delivery option, according to a company blog post. Almost 12 million people in Northern California can use its next-day service, it said.

Google is expanding in e-commerce and allying with retailers to compete with Amazon as it seeks to boost growth and lower its dependence on Web search, which now accounts for most of revenue. The Mountain View, California-based company is adding more stores and in August extended a mobile-advertising feature that shows what products are available nearby when users search for items.

Membership in Google Express costs $95 a year or $10 a month while consumers can also choose to pay as they go for $4.99 per eligible order. Same-day or overnight shipping for eligible items that cost more than $15 is free, according to the blog post.

Google has added 16 new merchants to the service in the last few months including Barnes & Noble Inc., PetSmart Inc. and 1-800-Flowers.com Inc., it said.

By Aaron Clark, with assistance from Brian Womack; editors: Michael Tighe, Robert Fenner, Dave McCombs.