Online sales for the key holiday retail day of "Cyber Monday" were on track for a record, helped by surging smartphone shopping, market trackers said.
The Adobe Digital Index showed that sales in the first 10 hours of the day were $490 million, up 14 percent from a year ago. That puts sales on track for $3 billion, Adobe said.
The big jump in online sales may have caught some retailers off guard. Retail giant Target's website went down briefly, as did the payments service PayPal, and some high-demand items were selling out.
"Out of stock is at an all time high this Cyber Monday—15 out of 100 product views are returning out of stock messages," Adobe said.
Cyber Monday tradition dates back a decade when retailers launched promotions for the Monday after the US Thanksgiving holiday—when many people took advantage of high-speed Internet at their offices.
The day still features numerous promotions and discounts for shoppers looking for an early start for holiday gift-giving.
According to Adobe, 53 percent of online retail traffic came from mobile devices, as did 32 percent of sales.
"US consumers have turned into digital shopping ninjas this holiday season as retailers continue to adjust to a huge influx of smartphone shoppers," said Adobe analyst Tamara Gaffney in a statement.
Some of the hot items according to Adobe included the Star Wars R2D2 Interactive Robotic Droid, the PlayStation 4 bundled with the Disney Star Wars game, and the Xbox One bundled with the Fallout 4 game.
Adobe said online sales between the Thanksgiving holiday Thursday and Sunday morning totaled $8.03 billion, a 17 percent increase from last year.
IBM meanwhile predicted Cyber Monday online sales would grow by more than 18 percent from last year, led by big-ticket items such as Samsung, Sony and LG televisions as well as Apple Watch and Beats headphones.
Cyber Monday was set to break the record for US ecommerce sales but it was dwarfed by the big November 11 "Singles Holiday" in China which generated some $14 billion in sales, according to online giant Alibaba.