(Bloomberg) -- US consumers spent $6.4 billion online in the first 24 hours of Amazon.com Inc.’s Prime Day, according to Adobe Inc. That’s up 6% from a year ago but fell short of estimates for even stronger growth as shoppers hunt for bargains. 

The 48-hour event, now in its 9th year, began Tuesday and runs through Wednesday. The promotions are designed to help Amazon grab new paying customers and deepen its relationship with existing ones before the holiday season. 

The research firm Numerator reported that the event was off to a strong start. As of 8 a.m. New York time, the average order size was $56.64, up 7% from a year ago, Numerator said Wednesday. Home goods and household essentials were the best-selling categories. Adobe said about 6% of orders were made using buy now, pay later services, up almost 20% from 2022.

Amazon shares rose 1.6% at 9:56 a.m. in New York.

Adobe earlier forecast US e-commerce sales would rise 9.5% during the sale. Worldwide, shoppers will spend an estimated $12.9 billion on Amazon during the event, up about 11% from last year, according to Insider Intelligence.

Amazon launched Prime Day in 2015 to attract new subscribers who pay $139 a year for shipping discounts, video streaming and other perks. About 167 million Amazon shoppers in the US had Prime memberships as of March, unchanged from a year earlier, according to market research firm Consumer Intelligence Research Partners.

The company this year launched “invite-only” promotions that let shoppers register interest in a deal and receive a unique link to purchase items that are still available, an effort to counter buyer disappointment when some the best deals disappear within seconds.

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