NEW YORK (CNN/Money) - Electronics retailer Best Buy's online store shut down midday Wednesday in what at least one Web site monitoring firm has called an "unplanned outage."

According to Ken Godskind, vice president of marketing for AlertSite.com, Bestbuy.com displayed a "store unavailable" page that the AlertSite's system first recognized at 12:36 p.m. ET.

Best Buy (Research) confirmed to CNN/Money that the company was experiencing a "systems problem" with its Web site.

"This was an unplanned outage and it's not related to volume or bandwidth," said Dawn Bryant, spokeswoman for Best Buy. "We're hoping to have it up soon."

The Web site was still displaying the same "store unavailable" page at 3:30 p.m. ET.

A message on the Web site said that customers would not be able to shop online because "we are making updates to our online store. Please come back soon. Use the links below to learn about in-store specials and more. We apologize for the inconvenience."

"Usually, updates are done very early in the morning and not in the middle of the day," said Godskind. "My guess is that this is an unplanned outage and the message on the Web site is a graceful reaction to an unplanned event. It's not something retailers want to see happening close to the holiday shopping season."

"On Nov. 9, only a few days before Christmas, is not the best time to have an outage like this," said Jupiter Research analyst Patti Freeman Evans.

"This is hugely undesirable for Best Buy," she said. "But as a big, sophisticated online seller with so many moving parts, something like this can happen for any number of reasons. It's not likely to happen often because Best Buy does have checks and balances in place to prevent that."