(Reuters) - Amazon.com Inc said it shipped more than 1 billion items worldwide this holiday season, which the top online retailer called its best ever, and its shares rose 1.6 percent in afternoon trade.

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The Amazon Echo home assistant and its smaller version, Echo Dot, topped the best-sellers list, said Jeff Wilke, chief executive of Amazon’s worldwide consumer division, in a press release.

“Despite our best efforts and ramped-up production, we still had trouble keeping them in stock,” he said.

Sales of voice-controlled Echo devices were nine times more than they were during last year’s holiday season, the company said. Amazon did not disclose comparable sales figures from a year earlier.

“It’s all relative to other numbers that they’ve never told us,” said analyst Jan Dawson of Jackdaw Research.

Amazon likely sold between 4 million and 5 million devices this year to date with Alexa, the voice-controlled assistant on the Echo, estimated Morningstar analyst R.J. Hottovy in a research note. Shoppers can command the Echo to perform a host of tasks, from playing music to turning on Christmas lights.

“While Amazon’s device sales are still relatively small growth drivers currently, we believe the proliferation of these devices will drive more ubiquitous use of Amazon services over time,” said Baird Equity Research analyst Colin Sebastian in a note, pointing to customers ordering more items by speaking to the Echo.

More than 72 percent of Amazon’s customers worldwide shopped through mobile devices, the company added, and 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.

Alexa and Amazon Dash, a one-button ordering service, are making it easier for shoppers to “skip the trip,” and will put more pressure on rival retailers as they try to garner in-store and web traffic, Perkins said.

Other best sellers on Amazon included 72-pack Keurig K-Cups, the movie “Finding Dory,” Samsung Electronics 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 shares rose $12.33, or 1.6 percent, trading at $772.92 at 1:58 p.m. EST (18:58 GMT).