Online US shopping for Black Friday deals rose to $US3 billion ($3.3 billion) during a two-day period beginning on Thursday, with tablets and mobile phones as top must-have items, estimates showed.
Online purchases reached $US1.93 billion on Friday itself, the unofficial start of the US retail sector's holiday season.
That marked a 39 per cent increase over last year, said software maker Adobe, which analysed 400 million visits on some 2000 American shopping websites.
Holiday shopping traditionally accounts for 20 to 40 per cent of an individual retailer's annual sales, the National Retail Federation said.
Early online Black Friday sales, which began on Thursday, the US Thanksgiving holiday, reached $US1.06 billion, up 18 per cent from last year, Adobe said.
IBM also reported increased numbers in overall online sales as it looked at 800 merchant websites.
IBM said internet sales rose 19.7 per cent over last year on Thanksgiving and 19 per cent on Black Friday, with orders averaging $US135.27, a 2.2 per cent increase compared with last year.
Online shoppers may have been wise to avoid stores, with reports of fistfights, a stabbing and a shooting as people elbowed their way through crowded shopping floors to snatch heavily discounted items.
Purchases of smartphones, tablets and other mobile devices accounted for 24.2 per cent of online sales, Adobe said. Tablets represented 15.6 per cent of online sales while smartphones represented 8.6 per cent. IBM also found that mobile devices accounted for 21.8 per cent of sales.
Adobe said that of the $US3 billion in total online sales over the two days, $US417 million was done on iPads and $US126 million was done on iPhones, while Android phones were used to buy $106 million in purchases and Android tablets accounted for $US42 million.
IBM said tablets were used for 14.4 per cent of online sales, against 7.2 per cent on smartphones. On average, tablet users each spent $US132.75 and smartphone users spent $US115.63. The company also found that iPad and iPhone users spent more, shelling out an average of $US127.92, compared with $US105.20 for users of Android.
Adobe agreed that Apple users spent more than people using Android devices.
IBM also said purchases made from Apple devices accounted for 18.1 per cent of total online sales, against 3.5 per cent for Android devices.