Amazon's UK website said it had seen sales on Christmas Day increase by 263% over the last five years.
It expects today to be its busiest Christmas Day to date, partly due to the growth in home broadband and the popularity of tablets and smartphones.
The retailer is launching its Boxing Day deals today, which include clearance offers and "lightning deals" for a limited time and quantity of stock.
Trends seen on past Christmas Days on Amazon include an 11am rush for last minute gift cards, the spending of gift cards at midday and sofa surfing at 8.15pm.
Amazon's vice president of EU retail, Xavier Garambois, said: "The digital revolution has certainly played a part in this growth and Christmas Day is our biggest day of the year for MP3 and Kindle Book downloads, as many people are buying content from new devices that they have just received.
"It's not just digital items though, we are seeing purchases of everything from baby products to women's clothing rapidly growing on Christmas Day. Many customers are shopping on Christmas Day in a way that has previously only been seen in the retail industry on Boxing Day."
According to MoneySupermarket.com, shoppers in the UK are set to spend a total of 2.9 billion in the Boxing Day sales.
A poll for the website found almost four million Britons (8%) plan to head to the high street on Boxing Day in addition to more than five million (10%) who will be searching online.
Furniture Village said visits to its website on Christmas Day last year peaked at 25,000 at 4pm, with that figure increasing to 50,000 on Boxing Day, suggesting that the majority of customers researched products online before buying from high street stores.
Analysts Experian predict that Christmas 2012 will be the "biggest and busiest ever" for online retailers in the UK, with visits to retail websites expected to reach 126 million tomorrow, up 31% on 2011.
They believe consumers will spend 472.5 million on Boxing Day bargains.
Experian's digital insight manager James Murray said: "Christmas 2012 is on track to be another record-breaker for online retail, outstripping 2011 on all fronts.
"The current market trends suggest that in the UK, Boxing Day will be the biggest day for online retail, with an estimated 126 million visits to online retail outlets and a massive 17 million hours spent online shopping on this day alone."
Chris Webster, a spokesman for technology analysts Capgemini, said: "Online tills will be ringing all the way from Christmas Eve to Boxing Day, including a massive 300 million spent on Christmas morning itself.
"Christmas Day will see a surge in online sales as new tablets and smartphones are put through their paces and vouchers are cashed in for virtual goods such as movies and music. This year we're as likely to be downloading Queen's Greatest Hits as watching the Queen's speech."
While the January sales started early online, early figures suggested British retailers would be shunning the shops from Boxing Day and beyond.
Almost half (47%) were not planning on buying anything in the post-Christmas sales, according to research by comparison website Pricerunner.
Meanwhile, high-street spending was "acceptable but not exceptional" this festive period, according to the British Retail Consortium.
As more shoppers flocked to the web rather than the shops to buy presents, high-street retailers faced the threat of closure, business recovery group Begbies Traynor warned.
Almost 140 firms were in a critical condition in the fourth quarter, meaning they are on the brink of collapse, while more than 13,700 were in "significant" distress - up 35% during the three months to December 17, the Begbies Traynor report said.
But the BRC's head of media and campaigns Richard Dodd said poor accessibility on high streets, a lack of parking and weak consumer demand were to blame rather than an increase in online shopping.
But he acknowledged that some high-street retailers would "undoubtedly" fail after Christmas.
"Retail sales over the weekend have been up to expectations but expectations were relatively modest," said Mr Dodd.
"Christmas will turn out to be acceptable but not exceptional."
He went on: "There are a lot of myths around online retail. Ten per cent of overall retailing over the year comes from online shopping and actually it presents lots of opportunities for the retail sector."