NEW YORK (CNN/Money) - A technical glitch caused online retailer Amazon.com to suffer at least two periods of extended slowdowns Thursday, one during late morning and a second during the peak lunch-time browsing period.

According to Web site monitoring firm AlertSite.com, the first slowdown occurred between 9:30 to 10 a.m. ET, during which time the Web site was available to 82 percent of users.

The situation became worse for a 40-minute period between 1:20 p.m. to 2 p.m. ET, when the site was available to just 25 percent of users, said Ken Godskind, vice president of marketing for AlertSite.com.

"What started out as a small error in the morning is turning into somewhat of a bigger matter," Godskind told CNN/Money. "When your Web site is the face of the entire company, that kind of an error is a big deal." Godskind estimates that the 40-minute slowdown in the afternoon probably affected traffic of about a million impressions to the site.

Patty Smith, spokeswoman for Amazon.com (Research), attributed the slowdown to a "technical problem."

"When you have a complex infrastructure, despite our best efforts, we still experience slowdowns occasionally but we try to minimize them," Smith said.

Vadim Mazo, chief technology officer with Dotcom-Monitor, agreed with Godskind that Amazon.com's troubles Thursday could impact overall sales for the day. "There were definitely periods of longer-than-usual response times," he said. "If just one page is slow, a potential customer might still wait around until it downloads. But if the entire site is slow, that means lost orders."

Mazo said the response time to access Amazon.com is typically between 2 to 4 seconds. But he noted that during the two intervals Thursday, it took users more than one to two minutes to access the site. "It was very, very slow."