Amazon suffered glitches in the opening minutes 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.

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 gave up nearly all of those gains by 3:20 ET.

Some users saw an error page featuring the “dogs of Amazon” and were never able 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.

Prime Day was projected to break records again this year, surpassing even the “tens of millions” of Prime members who shopped the discounts last year. Wall Street expected higher sales and a higher share price for Amazon as a result.

Amazon’s e-commerce sales in the U.S. are expected to reach a staggering $258.2 billion this year, up nearly 30 percent from a year ago, according to a new survey from eMarketer that looks at the company’s sales by product category.

That means Amazon is expected to capture nearly half of the U.S. e-commerce market by the end of 2018, eMarketer said. The company ended 2017 with about 44 percent of the market.

On Prime Day, industry analysts estimate the company could ring up as least $3.4 billion. This is the first Prime Day that Amazon owns Whole Foods, which has its own deals running through the week.

Amazon did not immediately respond to requests for comment from CNBC about the glitches.

This is developing news. Please check back for updates.