Amazon.com Inc. (MAZN.O) shoppers are snatching up potato chips, crackers, toilet paper and other non-perishable grocery store items to take advantage of the online retailer’s Prime Day deals, which could be bad news for Costco Wholesale Corp. (COST.O) and Walmart Inc (WMT.N).

Sales of consumable products on Amazon during the first nine hours of Prime Day -- a two-day sale that began Monday -- are about triple what they are on a typical sales day, according to CommerceIQ, which helps hundreds of consumer brands sell products on the e-commerce site.

The results show Prime Day’s appeal stretches beyond electronics, appliances and other big-ticket purchases shoppers usually put off until there’s a big promotion. Sales of car seats, appliances and toys were up four to five times a typical day, according to CommerceIQ, which is about the usual rate for a sales event.

Shoppers will spend US$5.8 billion on Amazon over the two days, according to an estimate from Coresight Research. That’s an 11 per cent increase from last year’s 36-hour sale when converted to spending per hour. Amazon launched Prime Day in 2015 as a way to lure new Prime members, who pay monthly or yearly fees in exchange for shipping discounts and other perks like video streaming.

The uptick in spending shows Amazon Prime Day continues to have strong appeal to shoppers despite competing sales events offered by rivals from Walmart to Target Corp. (TGT.N) and EBay Inc. (EBAY.O).

Amazon doesn’t disclose specific sales information about Prime Day. Some companies are able to gain insights through their own sales on the site or estimations based on sales rankings and other information Amazon discloses.