Amazon suffered glitches at the start of Prime Day on Monday, slowing sales on the e-retailer's biggest shopping day of the year. Amazon's annual shopping holiday kicked off at 3 pm E.T. and runs for 36 hours, the longest Prime Day yet. Shoppers reported several errors — on both the desktop site and the mobile app. Amazon did not immediately respond to requests for comment from CNBC about the glitches, but later posted on Twitter: "Some customers are having difficulty shopping, and we're working to resolve the issue quickly. Many are shopping successfully — in the first hour of Prime Day in the U.S., customers have ordered more items compared to the first hour last year." TWEET Shares of Amazon fell off session highs immediately following the rocky start to Prime Day. The stock had gained more than 1.5 percent earlier Monday, reaching an all-time-high of $1,841.95. But it closed the day up only about half a percent at $1,822.49, and was falling about 1 percent in after-hours trading.

Source: Amazon.com

Some users saw an error page featuring the "dogs of Amazon" and were initially unable to enter the site. Some got caught in a loop of pages urging them to "Shop all deals." Clicking the entry link for a specific category returned the user to the first page urging them to "Shop all deals." Some users successfully added items to their cart, only to receive an error message when trying to checkout and complete the purchase. Other users saw the "deals" page and "Shop all deals" button disappear entirely.