An Amazon delivery worker pulls a delivery cart full of packages during its annual Prime Day promotion in New York City, June 21, 2021.Brendan McDermid | ReutersAmazon said Monday it's adding a handful of retail brands to its same-day delivery offering for Prime members.To start, Amazon is offering same-day delivery from apparel brands PacSun, Diesel, and Superdry, as well as vitamin retailer GNC, in 10 cities across the U.S. The service is free for Prime members when they spend $25 or more, or $2.99 if they spend less than $25, Amazon said.Some of the participating retailers also give shoppers the option to order items online and pick them up at the store.CNBC previously reported Amazon was testing a similar model with its Flex delivery drivers, wherein they'd fetch packages from mall-based retailers and drop them off at customers' doorsteps.Amazon continues to invest heavily to make one-day and, in some areas, same-day, delivery the default for its Prime members. The company has expanded the number of one-day eligible products, and it now has "thousands" of items that can be delivered in a few hours.Consumers are increasingly demanding faster and faster delivery speeds from online retailers, as evidenced by the explosion of ultrafast grocery platforms in the last year. Retailers have also jumped on the trend by partnering with on-demand delivery providers like DoorDash, Uber's Postmates, Instacart, UPS' Roadie, as well as Target's Shipt. The partnerships mean that consumers can often get a new t-shirt or dress in a matter of hours.With the new partnership, retailers will fulfill orders from inventory in their stores, and a Flex delivery driver will pick them up from the retailer. Doing so allows Amazon to get online purchases to shoppers' doorsteps even faster.Amazon isn't the only company looking beyond warehouses to fulfill e-commerce orders. Walmart and Target are tapping into their large brick-and-mortar footprints to speed deliveries with the hopes of expanding their e-commerce market share.WATCH: Watch the first look at Amazon and Rivian's electric delivery vans
Amazon launches same-day delivery for some retail brands.