U.S. supermarket chain Kroger said on Tuesday it has started using unmanned autonomous vehicles to deliver groceries Scottsdale, Arizona in partnership with Silicon Valley startup Nuro.

Since August, the companies have operated a self-driving grocery delivery service in Scottsdale, AZ with an autonomous Prius fleet accompanied by vehicle operators. The autonomous vehicles have completed nearly one thousand deliveries to the general public.

With today's launch, the fleet is expanding to include Nuro's custom unmanned vehicle known as the R1. The R1 travels on public roads and has no driver, no passengers and only transports goods. Nuro has been developing the R1 since 2016, and announced its partnership with Kroger in June.

Delivery service details:

• Where: Fry's Food Stores (single location): 7770 East McDowell Road, Scottsdale, AZ 85257
• When: Customers can place delivery orders immediately, for delivery 7 days a week
• How: Customers shop via frysfood.com or the Fry's Food Stores mobile app and place their order based on slot availability
• What: Grocery orders can be scheduled for same-day or next-day delivery by Nuro's fleet of self-driving vehicles, now featuring the custom unmanned R1 as well as self-driving Prius vehicles
• Price: $5.95 flat fee; no minimum order

Walmart Inc and Amazon.com Inc have also invested heavily in their delivery operations by expanding their offerings and shortening delivery times.

Walmart, Ford Motor Co and delivery service Postmates Inc said last month they would collaborate to deliver groceries and other goods to Walmart customers and that could someday use autonomous vehicles.