Google expands Amazon Prime rival to more cities

As it seeks to get a bigger slice of Americans' spending, Google just ramped up the delivery wars by expanding its same-day service.

The tech giant announced its Google Express service will serve three more cities—Chicago, Boston and Washington. It was already available in the San Francisco area, West Los Angeles and Manhattan.

Over the next couple months, 16 more companies will also join the list of stores available for same-day delivery, including Costco, Target, Staples and Whole Foods Market. Bay Area shoppers who are at least 21 years old can now order alcohol, too.

Google Express
Source: Google Express

Google Express' expansion places it in more direct competition with Amazon.com's Prime services, which offer free two-day delivery to paid members on eligible items.

Read MoreAmazon.com to open first physical store in Manhattan

Despite the expansion, the Google coverage area remains relatively limited with more than 7 million people able to access same-day delivery.

Google Express members get free same-day and overnight delivery on eligible orders ringing up more than $15. Membership can be shared with someone in the same household.

Read MoreGoogle axes 170,000 'right to be forgotten' links

Memberships costs $95 per year or $10 per month, but new members can get a free three-month trial.