Amazon (AMZN) - Get Report on Tuesday said it would add free two-hour shipping to its Alexa voice assistant, as the e-commerce giant encourages shoppers to get more comfortable placing orders using just their voice. 

Prime Now two-hour shipping is only available in 30 cities and for select items, such as "daily essentials," the company said in a statement. Users can also order wine, beer and liquor via Alexa's Prime Now shipping, but only in certain cities.

Alexa is enabled in Amazon Echo, Echo Dot, Tap, Fire Tablet, Fire TV and, as of last week, iPhone and iPad devices via the Amazon shopping app. Amazon emphasized that voice-enabled purchases and Prime Now shipping bring added convenience for shoppers by allowing them to place orders if they're "too sick to get out of bed."

When Amazon first released its range of Echo products, the company's primary objective was to familiarize users with voice-activated devices in general. In the past six months, consumer awareness of Alexa devices (such as the Echo Dot, which was the top-selling product on Amazon last holiday season) has surged to 77% from 33%, demonstrating that it's headed toward mass adoption.

Amazon's next move is to own the voice-activated e-commerce market, said Ken Cassar, principal analyst at e-commerce analytics firm Slice Intelligence. The Echo devices and Alexa voice assistant technology have made it so that users are engaging with the "Amazon ecosystem" more regularly, Cassar noted, meaning that they might be more likely to make a purchase. 

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Last monthAlphabet's (GOOGL) - Get Report Google Home, which is a growing competitor to the Amazon Echo, also began allowing users to shop from about 50 U.S. retailers. 

RBC Capital Markets analyst Mark Mahaney said in a recent note that "voice shopping and ordering is still rather unfamiliar" for most people. He added that most Alexa device owners use the products for "lean back entertainment," such as playing music and checking the weather, rather than ordering items or calling an Uber.

Nevertheless, he said that Alexa could generate as much as $10 billion in revenue by 2020, with voice-driven shopping accounting for half that number, as users gradually become more comfortable with it. 

RBC's data also indicated that the "vast majority" of Alexa device owners are also Prime members and that most users were ordering electronics and apparel, followed by consumer packaged goods and grocery items. So Amazon's addition of free two-hour shipping is unlikely to fall on deaf ears.

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