SEATTLE — Stepping up its challenge to brick-and-mortar retailers, Amazon.com launched a new shipping feature Thursday that will let shoppers buy a product on its website by noon and have it delivered by 9 p.m., seven days a week.

The new service, called Prime Free Same-Day Delivery, will be available on more than 1 million products and in 14 metropolitan areas in the United States. There will be no shipping cost for members of Amazon’s $99-a-year Prime service, as long as the order tops $35.

Amazon introduced same-day shipping in seven markets in 2009 and has expanded it since then. But Prime customers have had to pay an extra $5.99 per order for the expedited shipping. (They’ll still have to pay $5.99 for same-day delivery if their order is less than $35.) Non-Prime shoppers will continue to pay $8.99 per order and 99 cents per item for same-day delivery in the markets where it’s available.