Amazon is expanding its same-day grocery delivery service to 1,000 cities and towns across the U.S., the company said Wednesday.

Amazon has positioned itself as America's most prominent shopping retailer, and a large part of that dominance is the two-day shipping offered for most items on the site. Customers with Amazon Prime are able to have items to their door within 48 hours of ordering,

While the retailer’s same-day delivery expansion leverages its enormous reach online, its fractional brick-and-mortar presence remains a central liability, industry analysts said.