Amazon.com's third annual Prime Day event turned out to be the biggest day ever for the e-commerce giant, with sales surpassing traditional retailing blowouts like Black Friday and Cyber Monday.
The most popular purchase over the 30-hour event was Amazon's Echo Dot mini-speaker, which was discounted by 30 per cent.
Having extended the shopping spree by six hours, Amazon said the event grew by more than 60 per cent compared with the same 30-hour period last year.
The promotion also saw an influx of new Prime members, Amazon said.
Amazon Prime costs US$99 ($136) a year and provides perks such as free two-day shipping for US customers on many items as well as music and video streaming.
"Tens of millions" of Prime members made a purchase during the event this year, more than 50 per cent higher than last year, Amazon said in a statement.
The Seattle-based company uses the July sales event to promote Prime membership and convert the occasional Amazon shopper into a devotee.
But the Prime business model is under increasing competition. Wal-Mart Stores in January began offering free two-day shipping on millions of items without a membership.
And Macy's offered free shipping on all orders, regardless of price, Tuesday only.
Amazon used steep discounts to turn its Echo speaker line into a best seller.
Even if Amazon loses money on the device sales, it gets a toehold for its Alexa platform to become more connected to shoppers who can use it to check the weather, stream music, hail an Uber, order pizza - and of course buy more from Amazon - by voice command.
The original Echo model was discounted 50 per cent to US$90.
Amazon said Prime members purchased seven times more Amazon Echo devices globally than during the event last year.
Amazon has been introducing new lines of the speakers that have screens and can take pictures.
The company is betting heavily on the devices to keep ahead of Google and Apple in the emerging field of voice-based computing.
"They see voice as the third-generation platform for ordering things online," said Matt Sargent, senior vice president of retail at the Minneapolis consulting firm Frank N. Magid Associates. "They want these devices in as many places as possible in case people shift from ordering on mobile devices to ordering with their voices."