Amazon.com is expanding its one-hour delivery Prime Now service for household products to Baltimore and Miami. The service, which includes products such as paper towels, shampoo, books, toys and batteries, works through a mobile app and is already available in sections of New York City. Starting Thursday, only certain zip codes within Baltimore and Miami will be included, but the company plans to further expand within each city soon. The delivery service is available to customers enrolled in Amazon Prime, a membership service that costs $99 a year and includes free two-day shipping on a range of products and instant content streaming options. In Miami and Baltimore, Prime Now is available from 8 a.m. to 10 p.m., seven days a week. Two-hour delivery is free and one-hour delivery is available in select zip codes for $7.99. The Seattle-based online retailer said it plans to roll out the Prime Now service in more cities this year. ‘Since launching, we've seen high demand on everything from essentials like water and paper towels to more surprising deliveries like getting a customer a hard-to-find, top-selling toy in 23 minutes,’ said Dave Clark, Amazon's senior vice president of worldwide operations, in a statement. The company has been investing in upgrading and expanding its distribution network in an effort to speed up delivery times.