NEW YORK (AP) -- Amazon is now rolling out a service where its Prime members can order their blueberries and milk at the same time as their batteries, T-shirts and other basic items.

The online juggernaut said Wednesday that customers in more than 1,000 cities and towns now have access to fresh groceries with its free same-day delivery service on orders over $25 for Prime members, with plans to reach over 2,300 by the end of the year.

The move marks one of the most significant grocery expansions for the online retailer as Amazon introduces thousands of perishable food items into its existing logistics network. The expansion is expected to put more pressure on grocery delivery services offered by such rivals as Walmart, Kroger and Target, which all saw their shares take a hit in early trading Wednesday.

Amazon's shares rose 1%.

Amazon said that if an order doesn't meet the minimum, members can still choose same-day delivery for a $2.99 fee. For customers without a Prime membership, the service is available with a $12.99 fee, regardless of order size.

In the past, Prime subscribers' grocery orders were fulfilled through Amazon Fresh or Whole Foods.

Prime members pay $14.99 monthly or $149 annually.

"We're continuously innovating to make grocery shopping simpler, faster, and more affordable for our customers, especially Prime members," said Doug Herrington, CEO of Worldwide Amazon Stores, in a statement. "By introducing fresh groceries into our Same-Day Delivery service, we're creating a quick and easy experience for customers. "

Herrington noted that customers can order milk alongside electronics; oranges, apples, and potatoes with a mystery novel; and frozen pizza at the same time as tools for their next home improvement project--and check out with one cart and have everything delivered to their doorstep within hours.

Amazon said it generated over $100 billion in gross sales of groceries and household essentials last year not including sales from Whole Foods Market and Amazon Fresh.

In June, Amazon said it was investing more than $4 billion to triple the size of its delivery network by 2026, with a focus on small towns and rural communities across the country.

It also noted that it's using artificial intelligence to help it predict local customer preferences so it can stock popular items alongside items targeted for specific communities.