Shopaholics have been binge-buying online as the pre-Christmas spending splurge continues.

Cyber Monday could have seen up to £650 million spent online within 24 hours, experts believe.

But with sales figures only released tomorrow it remains to be seen whether it surpasses the sales frenzy of Black Friday, which was marred by chaos that unfolded in some retail stores when bargain-hunters clashed over heavily discounted goods.

A new website that logs online sales says that the number of transactions was below that of Black Friday.

Postcode Anywhere's Big Data Labs, which analyses e-commerce sales in real-time based on the postcode entered by shoppers on websites, said there were 267,370 transactions up until 6pm today, compared to 404,835 in the same period on Friday.

Guy Mucklow, the company's chief executive and founder, said: "The Black Friday sales saw Britain's most savvy shoppers logging online in the early hours to secure the best bargains and spend their cash. It proved to be the busiest e-commerce shopping day on record for many of the UK's retailers in the lead up to Christmas.

"In comparison to Black Friday which saw almost 40,000 head online between 1pm and 2pm, our data showed that Cyber Monday attracted a much more modest haul of spenders with just over 30,000 people logging on at the same time today.

"It is clear that as Black Friday deals spanned across the course of the payday weekend, many shoppers were already spent by the time Cyber Monday landed."

Last year's Cyber Monday was Amazon UK's then busiest day of sales ever, with more than 4.1 million items ordered at a rate of around 47 per second, with sales peaking at 9.22pm.

But after it sold 5.5 million items through its UK website on Black Friday, Amazon said this year's Cyber Monday would have to be a "huge day" to beat it.

Experian Marketing Services said that it expected £649.6 million, or £451,000 per second, to be spent online today, an increase of £145 million (26%) over last Christmas.

But it expects that figure to be eclipsed by "Manic Monday" a week today, when it forecasts £676.5 million (£470,000 per minute) of sales.

James Miller, Experian's senior retail consultant, said: "Continuing a trend we identified last year, Cyber Monday will no longer be the busiest pre-Christmas online shopping day, with Manic Monday expected to take the lead.

"With increased confidence in the standard of delivery services and 'click and collect', we expect to see people break away from traditional shopping habits."

Sage Pay also predicted that online retailers would take just over £600 million today as website visits hit 125 million peaking at noon, with its own figures showing that the total amount spent by UK consumers on Cyber Monday grew 15% year-on-year in 2013.

Meanwhile, the Department for Business, Innovation and Skills (BIS) said research showed that 55% of the public find it difficult to support local small firms because they are often not online.

In addition, 52% of customers go straight to search engines when looking to buy from local businesses, nearly double the number that ask for word-of-mouth recommendations.

BIS said small businesses and sole traders could be missing out on total website sales in the UK worth £164 billion without a digital presence.