It has been the best holiday season for Amazon, here’s why

Amazon.com Inc said it had its best-ever holiday season, shipping more than one billion items worldwide through its Prime membership program.

The company said on Tuesday more than 72 percent of its customers worldwide shopped through mobile devices, adding that Dec. 19 was the busiest shopping day this holiday season.

The Amazon Echo home assistant and its smaller version, Echo Dot, were best sellers, said Jeff Wilke, chief executive of Amazon's Worldwide Consumer division. "Despite our best efforts and ramped-up production, we still had trouble keeping them in stock," he said.

Other best sellers 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 Pokemon Sun and Pokemon Moon role-playing video games, the company said.

Amazon's shares were up 1.4 percent at $771.24 in morning trading.