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Workers retrieve boxes at an Amazon fulfillment center on Prime Day in Raleigh, North Carolina, U.S., on Monday, June 21, 2021.
Rachel Jessen | Bloomberg | Getty Images

The first day of Amazon‘s 48-hour Prime Day event is expected to have driven the most online sales over a 24-hour period so far this year, according to new data released Tuesday.

Sales during the first 24 hours of Amazon’s megasale, which kicked off at 3 a.m. ET on Monday, are set to surpass $5.6 billion, representing 8.7% growth year over year, according to an index tracked by Adobe Analytics, which looks at more than one trillion visits to U.S. retail sites and over 100 million items across 18 various product categories.

That would make Monday the biggest day for online spending to date in 2021, Adobe said, surpassing the $5.1 billion that consumers spent online over Thanksgiving Day last year.

“The first day of Prime Day successfully accelerated spending momentum for U.S. e-commerce to new heights, in an online retail environment that is already experiencing elevated level of growth due to the pandemic,” said Jason Woosley, vice president of commerce product and platform at Adobe.

The biggest discounts found on Amazon’s website on Monday were for toys, Adobe said, with prices dropping 12% on average. Appliances averaged a 5.2% discount, while electronics were marked down about 3%, Adobe said.

The firm said the best deals across all categories of products are expected to come later this year during the holidays.

This story is developing. Please check back for updates.