As Amazon (AMZN - Get Report) continues to expand its fast delivery service Prime Now, Uber is expanding its own alternative called UberRush.

Uber launched its delivery service in October with a few companies, offering to deliver their products quickly to consumers in New York, San Francisco and Chicago. On Thursday, Uber announced that it is expanding the service to more companies by creating an API, or application program interface, that companies like 1800Flowers (FLWS - Get Report) can use to easily add UberRush to their existing infrastructure and apps.

UberRush will charge merchants $5 to $7 to deliver orders, and it can work quietly in the background with customers not even being aware of the fact that Uber is handling the delivery. Customers would just order from a merchant's app like normal and then happen to receive the order from an UberRush delivery person.

With Amazon upping the stakes for retailers in terms of delivery time, traditional retailers are struggling to keep up on their own, and Uber may offer them a way out.

Right now, 1800Flowers, Nordstrom (JWN - Get Report) , T-Mobile (TMUS - Get Report) , Rent the Runway, and a few other retailers are using the API. Back-end companies like Curbside, which will shop for consumers at local stores, and Alphabet's (GOOG - Get Report) Google Express are also using the API. And Uber plans to offer the API to more companies in the future.

"We're hoping that one day through the UberRUSH API, getting anything in your city will be more affordable and reliable than getting in your car to pick it up yourself," Jason Droege, the head of UberEverything, wrote in a blog post.

Uber certainly isn't the only one trying to handle fast delivery in the on-demand economy. Startups such as Postmates, Instacart and Deliv are working on this, but probably more notable is Amazon's competition with Prime Now.

Amazon first announced Prime Now in 2014 and it now operates in 18 zip codes in the U.S.

While Prime Now started out as faster delivery for select products that are sold on Amazon.com, it has grown into a much larger endeavor. It now delivers from restaurants, local shops and grocery stores, and even local liquor stores.

Compared to other players, Amazon has the upper hand in a number of ways. First of all, it already has the back-end logistics in place for its core business, so it's starting from a much more advanced stage compared to a startup that's creating something from nothing. On top of that, Amazon already has loyal Prime members who are stuck in the Amazon ecosystem.

"They have you locked in, and it meets your needs easier than going outside," Greg Portell, a partner in A.T. Kearney's Consumer Products & Retail and Media Practices, said in an earlier interview. "They use their technology and the ecosystem they've created to essentially automate those decisions."