A massive surge of hits during one of the busiest shopping days of the year closed Walmart's website for much of Friday.
Walmart.com was paralysed under the pressure of online shoppers eager to cash in on heavy discounts during the so-called Black Friday shopping bonanza in the US.
Consumers struggled to access websites of many of the top online shops, but Walmart seemed to fare the worst.
The website started to feel the pressure from shoppers early in the morning, US Eastern time. During the day things became worse until Walmart took the website down, posting a temporary page saying: "Sorry, we're experiencing high volume".
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Linda Blakley, a Walmart spokeswoman, said: "Due to a higher-than-anticipated traffic surge, we made the decision to shut down the site temporarily." The website has now reopened and the problem is resolved.
Online shopping is typically heaviest during the run-up to Christmas, and Black Friday - the day after Thanksgiving and one of the biggest shopping days of the year - is seen as a good indicator of whether online retail stores are ready for heavy holiday traffic.
Amazon.com stumbled briefly on Thursday, after announcing the availability on the site of 1,000 deeply discounted Xbox 360 video game consoles, according to Keynote , which tracks website performance.
As bargain hunters converged on the site, some had trouble accessing Amazon for about 15 minutes, a Keynote spokesman said.