Amazon.com last night forecast key end of the year sales and profit that missed Wall Street targets, projecting revenue growth that would be the slowest in years.
This sent the shares of the world's largest online retailer down 8% in after-hours trade on Wall Street.
Amazon's third-quarter sales lagged estimates as well. Analysts said international results were disappointing and online competition was increasing.
The company blamed accounting changes and cautioned that it was being conservative with its outlook.
For years, Amazon has made expensive bets on new technology and programmes, like its $13.7 billion acquisition of Whole Foods in 2017 to storm the US grocery industry.
That has resulted in rollercoaster profits in the past, but revenue has largely grown at a breakneck pace as consumers shifted shopping online and away from brick-and-mortar stores.
Amazon's more subdued expectations for this year's holiday shopping season, which runs from the US Thanksgiving holiday in late November up to New Year's, was a particular surprise.
It forecast that fourth-quarter sales will rise between 10-20%, or up to $72.5 billion, while analysts were expecting $73.9 billion, according to Refinitiv data.
That would be Amazon's lowest quarterly sales growth since at least the start of 2016. In the last four quarters, sales increased between 29% and 43%.
Brian Olsavsky, Amazon's chief financial officer, said no fundamentals had changed, just some holiday timing in India and accounting differences.
"We're expecting a strong holiday season, so there's no message in our forward guidance against that," he said on a conference call with media. "We have everything ready to roll."
The company moved the recording of $300m in Prime subscription revenue from the fourth quarter to earlier periods in the year, he said.
In addition, Amazon faces a tougher year-over-year comparison because the Whole Foods deal closed in the third quarter of 2017, and the different timing of the holiday Diwali affected sales patterns, he said.
Analysts said the results reflected a shifting landscape with retailers holding their own against Amazon.
Despite slower sales growth, Amazon has steadily become more profitable.
Its third-quarter net income rose to $2.88 billion, or $5.75 per share, from $256m, or 52 cents per share, a year earlier.
Up to 53% of goods sold on Amazon now come from third-party merchants, the company said, marking a steady shift away from traditional retail where Amazon is the seller of a product.
That means the company is collecting less revenue but taking in a lucrative cut of others' sales - all the more profitable when merchants pay Amazon to handle their shipping. Seller services grew 31% to $10.4 billion in the third quarter.
More sellers are looking to Amazon to market their products, too - another highly profitable business.
Amazon appeals to advertisers because individuals generally are using the site to shop, unlike users browsing Alphabet's Google, the ads sales leader, to find general information or rival Facebook to see updates from their friends.
Amazon said revenue from the category and some other items grew 122% to $2.5 billion in the third quarter. Analysts were expecting $2.4 billion, according to Refinitiv data.
Olsavsky, the CFO, also said the company is operating more efficiently, hiring less than in the past and adding less warehousing space.
"We've really been able to cut back in a number of key areas," Olsavsky told reporters, citing cost improvements for cloud unit Amazon Web Services as well.
The world's biggest cloud business by revenue saw sales up 45.7% to $6.68 billion, narrowly edging past estimates of $6.67 billion.
