People buying food and last-minute presents face a race against time today as shops have been restricted to only six hours of opening.
Millions of shoppers are hitting the stores this weekend, and yesterday is expected to have become the busiest day of the year on the high street.
But those who may have left their shopping to the last minute will have to plan their excursions carefully, as there is not much time today in which to stock the fridge or get hold of those final few presents.
Supermarket chain Sainsbury's has recruited an extra 20,000 staff and sent 2,000 office workers to the shop floor to help meet demand this weekend.
A Sainsbury's spokeswoman said: "December 23 is always the busiest day for Christmas shopping, so to have it condensed into six hours will obviously pose challenges."
Sainsbury's expects to sell 225,000 bottles of champagne this weekend, and this Christmas will sell 90,000 turkeys, half a million kilograms of Christmas cheese, 6,500 tonnes of potatoes and 52 million sprouts.
Consumers are predicted to spend up to £5 billion over the course of the weekend as many retailers opened their doors until 11pm in the last dash to Christmas.
One credit card company alone said it expected to handle more than 30 million transactions yesterday.
Crowds flocked to London's West End and shopping centres up and down the country yesterday, braving wet and blustery conditions to make the most of early sales and discounts.
Streets were teeming with people in the capital - where Oxford Street, Regent Street and Bond Street were among the busiest hot-spots - and queues built up outside some shops before they opened their doors.
Meanwhile, growing numbers of consumers were still going online to snap up bargains.
Despite gloomy sales figures, cash spending was expected to be up on last year.
Visa Europe said customers were set to spend £1.26 billion on their Visa cards alone.
The company predicted it would process 31.9 million transactions yesterday, with 2pm to 3pm the busiest hour.
It said shoppers appeared to have saved up for a "spree" this weekend - dubbed "the big one" - with figures showing an incremental increase in spending in recent weeks.
The British Retail Consortium said yesterday would be the busier of the two days - primarily because of longer opening hours.
Spokesman Richard Dodd said: "There is no question that this will be the biggest spending weekend in the run-up to Christmas and therefore the biggest retail weekend.
"It's been a slow start for retailers because, whilst shopper numbers have been building week by week, they have been consistently down on 12 months ago."
But at Brent Cross shopping centre in north London, bosses said sales were likely to be bigger than ever before.
Centre manager Tom Nathan said: "With Christmas falling on Tuesday this year, and with schools breaking up late this year, this weekend is set to be the busiest shopping period, as more people leave their shopping later and later to buy gifts.
"These four days are predicted to be enormous for us in terms of sales - bigger than it's ever been."
Bluewater shopping centre in Kent said yesterday was its busiest day of the year, and expected more than 275,000 shoppers through the doors this weekend.
Elsewhere, Birmingham's Bullring centre welcomed the hordes and said 340,000 people were expected to visit its stores before Christmas Eve.
General manager Tim Walley said: "This Christmas we essentially have an extra weekend of trading in comparison to December 2011, so we're expecting a bumper weekend."
Similar scenes played out across the country. Shoppers thronged to the Westfield Derby shopping centre and Glasgow's Braehead mall ahead of opening, with the latter allowing customers in earlier than usual so they could queue inside the centre to escape the rain.
Its general manager, Peter Beagley, said: "By 10am our car parks were full and we had staff on duty directing cars to spaces when they became available."
A spokesman for Sheffield's Meadowhall mall said major stores such as M&S were enjoying particularly strong sales.
And at Union Square shopping centre in Aberdeen, footfall for Friday alone was up 12.1% on the same day last week.
But the Local Government Association (LGA) said confidence on the high street remained low.
Its annual Christmas survey found that 84% of town centre managers said confidence among shoppers had either not improved or worsened compared with this time last year.
The LGA suggested that the particularly cold and wet start to the winter could also be taking its toll on the number of shoppers visiting town centres.