Discount retailer Target Corp's website was down due to heavy traffic on Cyber Monday.

Shoppers looking for bargains on http://www.target.com/ were greeted with an error message: "So sorry, but high traffic's causing delays. If you wouldn't mind holding, we'll refresh automatically & get things going ASAP."

"Both traffic and order volumes are exceeding Target's Thursday Black Friday event ... To help manage the volume, we have been metering traffic to the site," Target spokeswoman Jamie Bastian said.

The company, the fourth largest U.S. retailer, said it was working to restore Target.com to full functionality.

Website performance monitor Catchpoint Systems said Target's website went down at 10:00 a.m. ET on Monday.

While the site was intermittently accessible for some users, items could not be added to the shopping cart. An error message read "There's a line for this item. So sorry for the delay."

Items including 4K ultra-high definition TV sets, Microsoft's Xbox One game consoles and even a 4-lb bag of granulated sugar could not be added to carts.

Twitter users were quick to express their displeasure. "Come on @Target get it together. How am I supposed to order anything on cyber Monday if you can't keep your website running?" Nikki_Ferrell tweeted.

In what Target has called its "Biggest, Boldest Plans" for Cyber Monday, the retailer is offering 15 percent discounts on almost all items on Target.com.

Target said on Friday it had "unprecedented results on Target.com" on Thanksgiving Day, and the company planned to offer free shipping on Target.com through Dec. 25.

Deals include 50 percent off on licensed kids' cameras and select Sennheiser in-ear headphones.

Upscale retailer Neiman Marcus's website was unavailable most of Friday, according to Catchpoint.

Other websites that have faced outages since early Thursday include L Brands Inc's Victoria's Secret and Foot Locker Inc, Catchpoint said.

About 121 million shoppers planned to shop online on Cyber Monday, down slightly from the 126.9 million who planned to participate last year, according to the National Retail Federation.

Target's shares were down 1.1 percent at $72.59 in late morning trading.