As online shopping becomes more popular over the Thanksgiving weekend, some retailers experienced outages amid the surge in traffic.
Costco's website went down entirely for a brief period of time early on Thanksgiving Day. Costco.com was experiencing "intermittent slow load and transaction times" starting late Wednesday, according to website performance monitor Catchpoint.
By Friday morning, Costco had a banner on its website that said "all Thanksgiving Day-only promotions have been extended into Friday, November 29th, WHILE SUPPLIES LAST."
Apparel retailer H&M's website was also down for a short period, less than 5 minutes, on Thanksgiving morning, Catchpoint said. The site later had intermittent outages again on Friday morning.
Nordstrom Rack customers reported some technical issues on social media on Black Friday.
The website monitor Catchpoint also said Home Depot's website had "slow load times" during the middle of the day on Thanksgiving.
Representatives from these companies didn't immediately respond to CNBC's requests for comment.
The stakes are high this weekend, leading into Cyber Monday. Even though Monday is traditionally the day that companies tout their steepest discounts online, more and more of that promotional activity has been seeping earlier into the holiday calendar.
Online retail sales on Thursday are expected to have surpassed $4 billion, according to Adobe Analytics, which monitors the online transactions of 80 of the top 100 web retailers in the U.S.
And the pressure is really intensified this holiday season, with six fewer days between Thanksgiving and Christmas compared with 2018, making for the shortest holiday shopping calendar possible.
In years past, around Black Friday, companies including Macy's, Target and Best Buy have all experienced web issues. ChannelAdvisor, a software platform for retailers, had estimated that retailers lose about 4% of a day's sales, each hour that a website is down.