Online giant Amazon plans to open a convenience store in Seattle where hungry customers will be able to grab sandwiches and go, without having to wait in line or use a checkout.

The American group unveiled the concept on Monday for its cashier less "Amazon Go" shop just over a year ago, saying the 170 square metre store would initially offer grocery products to its own employees before being opened to the public.

Early testing however revealed bugs, leading to a delay.

In a message on Sunday on its website, Amazon said it had created "the world's most advanced shopping technology so you never have to wait in line."

But if the rollout has taken some time, it's now ready to go.

People armed with the app are able to pick up items as they roam the store and place them directly in their bags. Instead, items are automatically added onto a customer's online account when they're removed from a shelf, or taken off if the item is put back.