Online retailers in the UK believe Monday could have been the busiest shopping day in history.
Recent years have seen online shopping figures consistently peaking on the first Monday in December, dubbed Mega Monday.
Visa Europe predicted £320m would be spent on its cards alone as online transactions top 6.8 million, an increase of 21% on 2011, making December 3 this year the busiest online shopping day in history.
It said: "A combination of pay day for the majority of consumers falling on the last Friday of the month and a weekend spent browsing the shops results in shoppers logging on to buy their gifts online on the subsequent Monday.
"All of these factors will result in consumers spending £222,222 per minute, making 4,722 transactions every 60 seconds."
Amazon said it expected its biggest single day, with orders peaking at 9.20pm.
Christopher North, managing director of Amazon in the UK, said: "Monday, December 3 could be the busiest day in the history of Amazon.co.uk, and we're preparing for it by hiring more than 10,000 seasonal employees across our eight UK fulfilment centres."
Marks & Spencer added that it expected Monday - which is also known as Cyber Monday - to be its busiest day of the year.
Sainsbury's Bank predicted a 1.3% rise in cash withdrawals compared with December last year, to reach a total of £11.1bn - which equates to more than £41,000 per second in the pre-Christmas peak.
December 21 is expected to be the busiest day for cash withdrawals, as it is traditionally when shoppers rush to buy last-minute gifts, while this Monday could give online retailers boosts of up to 70%.
Visa Europe commercial director Dr Steve Perry said: "On Mega Monday, people across the UK will go online and use their Visa cards to make 6.8 million transactions, the most in a single day in UK history.
"That's 21% more than in 2011, signalling that consumers are becoming increasingly accustomed to the advantages of shopping online for everyday purchases and special items, especially in the lead-up to Christmas."
Online analyst Experian expected UK consumers to make 115 million visits to retail websites on Mega Monday, an increase of 36% on last year.
The day comes just over a week after Black Friday - the US phenomenon which sees millions of shoppers flock to stores after Thanksgiving.
But Jon Copestake, retail analyst at the Economist Intelligence Unit, warned this year's Mega Monday might not be as successful as expected.
"Given double-digit online retail growth and a growing number price sensitive consumers comparing goods online, there is little doubt that 'Mega Monday' will be a key Christmas shopping fixture this year," he said.
"However, this impact could be diluted over time as UK shoppers latch onto promotions during the Black Friday and Cyber Monday sales of last week.
"Equally, online sales are becoming a feature of the entire shopping season and not just specific dates so 'Mega Monday' could ultimately span several days in the same way that Black Friday is beginning to over in the US."
The busiest shopping day on the high street often falls two days before Christmas Day, with the weekend of December 22 and 23 expected to draw peak numbers of shoppers this year.