Shoppers hoping to get their hands on one of Amazon.com Inc.’s Echo smart speakers before Christmas may come away disappointed.

Several of the e-commerce giant’s online stores in North America and Europe showed various models of the Alexa-powered line of gadgets temporarily out of stock on Monday, with shipment delayed to January or beyond in some places.

The Echo is the flagship device in Amazon’s growing line of consumer electronics and a fixture of the company’s advertisements during the holiday shopping season.

The company said it sold “millions” of Echo devices worldwide during the Thanksgiving holiday weekend and Cyber Monday and that the hockey puck-shaped Echo Dot was the bestselling product on Amazon during that period.

In the U.S., a product listing for the Echo Spot shows availability beginning Jan. 1. Other models were available for delivery beginning this week or, in the case of the Echo Plus, immediately. The Echo Dot is listed as unavailable in European countries in which Amazon sells the device, with estimated delivery dates ranging from January in Britain to as late as April in Germany.

Other retailers, including Best Buy Co. and Target Corp., had Echo Dot devices in stock for immediate shipment Monday. Amazon didn’t immediately comment on the shipment delays.

The company invented the voice-activated speaker category with the 2014 release of the Echo, a sleek plastic column that lets users play music, read the weather or news stories and control an array of internet-enabled home electronics.

Google entered the market in 2016 with its Home lineup of smart speakers, and 2018 marks the first year Apple Inc.’s rival HomePod will be on sale during the peak holiday shopping months.