Target Corp. struggled to handle a surge of e-commerce traffic on Cyber Monday, its biggest day for online sales, making the website inaccessible to some users.

Target.com offered 15 percent off almost everything on Monday, bringing a flood of traffic, the Minneapolis-based company said in a statement. To manage the volume, Target is metering traffic and working to ensure all customers are able to get on the website. So far, traffic and order volumes on Target.com have exceeded those on Black Friday, the company said.

Some visitors to Target's site were greeted with the message: "Please hold tight. So sorry, but high traffic's causing delays."

The outage comes at a bad time for Target, which is making a bigger play for e-commerce shoppers — especially on Cyber Monday. The event marks the first workday after the Thanksgiving weekend and typicallyis one of the busiest days for shopping online. To encourage customers to buy from Target's website, the retailer has been offering free shipping for the second holiday season in a row.

Neiman Marcus also suffered e-commerce trouble in recent days. The department-store chain's website crashed on Friday and Saturday, forcing it to extend Black Friday deals into Sunday. The company said on Monday that it didn't think hackers caused the problems.

"Our site outages caused an inconsistent shopping experience over the weekend," Ginger Reeder, a spokeswoman for Dallas-based Neiman Marcus, said in an email. "We have seen no reason to suspect outside interference or sabotage, however the exact cause of the outage has yet to be determined."

Online sales on Cyber Monday may rise at least 18 percent for all retailers from a year earlier, according to forecasts by International Business Machines Corp.