Walmart and Amazon are promising same-day deliveries in the $600bn US prescription medicines market, putting new pressure on drugstores and supermarkets that compete against the nation’s two largest retailers.

Walmart Inc. will start delivering prescriptions to US homes in as little as 30 minutes, a move that’s intended to grab a bigger slice of online spending and compete against Amazon.com Inc.

Walmart will start delivering medications in six states, but plans to offer prescription delivery in nearly every state by the end of January.

Walmart (NYSE:WMT) is adding a new service that has the potential to be disruptive. The retail giant will begin to deliver prescriptions to households in the U.S. in as little as 30 minutes. The service will see customers have the ability to add prescriptions and medication refills to their orders for groceries and other products.