Online retailers are expecting a final surge in orders as key pre-Christmas post deadlines draw near.
Online shoppers have been keen to avoid the High Street crush
Amazon has told customers to get orders in by midnight to ensure first-class deliveries arrive on time.
Meanwhile, sites such as garden centre Crocus.co.uk, which are offering special late deliveries, need orders to be made by 22 December.
Tight postal deadlines may mean a late boost for stores as last-minute shoppers head outside, experts suggest.
Royal Mail's suggested last posting dates in the UK, to make sure items arrive in time for Christmas, are 20 December for first class and 22 December for special delivery.
"Once the online deadline has passed and schools break up for Christmas, then we will get shoppers out for last-minute bits and pieces, " said Natasha Burton at market analysts FootFall.
But ahead of the final festive push, online sales are soaring as consumers hope to avoid the Christmas crush at traditional retailers.
An influx of online shoppers crashed the Argos website last week as it struggled to cope with huge volumes of shoppers and orders.
While the ordinary High Street saw a pick up in sales over the weekend, Saturday and Sunday had been "absolutely huge" for e-retailers, said industry body Interactive Media in Retailing Group (IMRG).
IMRG put the increase down to improved product lines, choice and investment in online stores.
Figures from the group estimate that some 24 million shoppers could spend as much as £5bn online in the run-up to Christmas.
And the postal service will be bearing the brunt, with reports suggesting it will handle 70 million online bought goods - 15 million more than last year.
Ahead of its midnight order deadline, Amazon said it was expecting a "strong last couple of days".
Even online garden centre Crocus has reported a late rush for festive goodies.
"It has been quite quiet up until last week, and since then it's got very, very busy - everyone must be leaving it to the last minute," a Crocus spokeswoman said.
Meanwhile, auction website eBay has revealed 2005 has been its busiest year on record - and expects it to remain so until final postal deadlines on Thursday.
"EBay is having its busiest Christmas ever and present auctions have been going strong since the beginning of December," the group said.
"The last day for special delivery is on Thursday, meaning last-minute Christmas auctions will need to end in the next two days so that the items can be sent off in time."
But that will not be the end of the story for the auction website, as it is perfectly placed for people to get rid of unwanted gifts.
"[Christmas] doesn't end there for us, as people flock to eBay to sell their unwanted pressies after Christmas Day," it added.
"Our research shows that most people expect to get around £50-worth of unwanted gifts and 65% of people are happy to sell them on."