Shares of Amazon rebounded Tuesday afternoon after a report said Prime Day sales on the e-tailer's third-party marketplace were up nearly 90 percent during the first 12 hours of the event from a year ago.

That's according to Feedvisor, an algorithmic pricing and business intelligence platform for online retailers, which monitors purchases made on Amazon's Marketplace. Revenues from third parties account for roughly two-thirds of Amazon's sales overall, with the rest going to Amazon's in-house brands.

Amazon shares had been falling less than 1 percent Tuesday morning, after the company suffered a series of glitches as Prime Day kicked off Monday at 3 p.m. ET. Most issues appeared to be resolved by Tuesday morning, and the stock was last up about 1.5 percent.

Amazon, which has a market value of about $894.6 billion, saw its stock trade as high $1,851.69 and as low as $1,797.38 by Tuesday afternoon.

Total cumulative orders on Amazon Marketplace for the first 12 hours of Prime Day were up 69 percent from a year ago, Feedvisor said. Compared with the same time period a week ago (3 p.m. ET on Monday, July 9, to 2:59 a.m. on Tuesday, July 10), total cumulative sales for third parties were up 80 percent, the group found.

Amazon said earlier Tuesday in an email to CNBC that "Prime Day sales in the US so far are bigger than ever – in fact, in the first ten hours Prime Day grew even faster, year-over-year, than the first ten hours last year." (Last year's Prime Day kicked off at 9 p.m. ET.)

Prime Day, started in 2015, is Amazon's busiest shopping event of the year. Prime Day sales in 2017 grew by 60 percent from the same 30-hour window in 2016, the company said a year ago.

By Tuesday morning, shoppers had already bought "millions" of Alexa-enabled devices, with the top-selling products being the Fire TV Stick with an Alexa Voice Remote, the Echo Dot, and the Fire 7 tablet with Alexa, according to the company.

Amazon also poked fun at its glitchy start (where photos of dogs were appearing on "Error" pages), saying: "It wasn’t all a walk in the (dog) park – we had a ruff start – we know some customers were temporarily unable to make purchases."

WATCH: Amazon Prime Day kicks off