Amazon.com said it had its best-ever holiday season, shipping more than one billion items worldwide through its Prime membership program.
The Amazon Echo home assistant and its smaller version, Echo Dot, topped the best-sellers list, the company said.
"Despite our best efforts and ramped-up production, we still had trouble keeping them in stock," said Jeff Wilke, chief executive of Amazon's Worldwide Consumer division.
Sales of Echo devices, controlled by Amazon's Alexa cloud-based system, were nine times more than last year's holiday season, the company said in a statement on Tuesday.
More than 72 percent of Amazon's customers worldwide shopped through mobile devices, the company said, adding that Dec. 19 was the busiest shopping day this holiday season.
"Prime customers are spending twice as much as other consumers using Amazon and helping to fuel rapid revenue growth that few retailers with only a fraction of Amazon's revenues are able to generate," Retail Metrics President Ken Perkins wrote in a note last week.
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Alexa and Amazon's Dash, Amazon's one-button ordering device, are making it increasingly easier for shoppers to "skip the trip," and will put additional pressure on retailers as they attempt to garner both in-store and Web traffic, Perkins said.
Other best sellers on Amazon included 72-pack Keurig K-Cups, the movie "Finding Dory", Samsung Electronic Co Ltd's Gear VR virtual reality headset and Nintendo Co Ltd's Pokémon Sun and Pokémon Moon role-playing video games, the company said.
Amazon's shares were up 1.4 percent at $771.24 in morning trading.