Amazon has started two-hour delivery from Whole Food stores to Amazon Prime members in four cities as part of a test of the service, which the retail giant plans to roll out nationwide. Service began recently in certain ZIP codes in Cincinnati, along with Austin, Dallas and Virginia Beach.

Not every item at Whole Foods locations will be available through the system, but most will be, including fresh produce, meat, seafood and flowers. The service will be available during regular store hours, Cincinnati.com reports.

The delivery system does not use Amazon's vast network of fulfillment centers. Rather, pickers will go down aisles of nearby Whole Foods stores to find the appropriate items. Thus the new service will require no additional industrial infrastructure on Amazon's part.

The move means direct competition for Instacart, which offers a similiar service. In 2016, Instacart inked a five-year deal to become Whole Foods' exclusive delivery service, but now that Whole Foods is owned by Amazon, the retailer is free to offer delivery from its own stores.

For now at least, Amazon is competing with Instacart via pricing, Business Insider reports. For a two-hour delivery, Instacart costs $5.99 on orders over $35, and sometimes prices are higher in busy times. One-hour delivery is $7.99, or shoppers can pay $149 each year for unlimited two-hour delivery on orders over $35.

Amazon Prime members will pay $4.99 for two-hour delivery, with orders over $35 delivered at no extra charge and $7.99 for one-hour delivery. Amazon Prime costs $99 a year.