Black Friday is on its way to becoming the biggest online shopping day in UK history as consumers shun the high street in search of bargains on the web.

Online retailers are reporting record-breaking sales from the first few hours of the bonanza making it likely that online retail sales in the UK will surpass £1 billion in one day.

By the end of the day retail analyst Experian-IMRG predicts that spending online will hit £1.07 billion, a 32% increase on last year's £810 million.

But the huge volume of traffic - Ebay is expecting nine million Britons to visit its website today - means that the websites of many retailers are struggling to cope.

Argos was among them with reports that its website has crashed several times and consumers have been confronted with a holding page saying 'Oops...Sorry to hold you up'.

Page load times for the UK retailer exceeded 10 seconds, in stark contrast to the 0.5 second page load time of its competitor Amazon, and beyond the two-second threshold which some analysts say makes consumers impatient and more likely to give up on a purchase.

Frustrated shoppers complained about the Argos website, with one saying on Twitter: "10 min queue online, then it told me 8 days for delivery with no option for 24 hour, and then it crashed."

Another frustrated user tweeted: "shouldn't advertise doing Black Friday if your website can't handle it. Trying to pay and keeps crashing."

Other retailers being singled out on social media for slow websites include fashion hub Boohoo.com, Boots, River Island and Debenhams.

Multiple errors on the Tesco website have also been reported, and between 10am and 11am the website slowed to an 8.4 second page load time.

Tesco denied anything was wrong saying on Twitter: "Our website is fully operational. We're very happy with our site speed. Feedback from customers today has been very positive #justsaying."

Online retailer very.co.uk said it had more than half a million users visit its site by 9am having launched sales at midnight, with a surge in traffic at 7am when its hourly deals went live.

The company is predicting at least 250,000 orders by the end of the day with beauty and electrical products such as hair curlers and games consoles proving to be the best selling products so far.

Currys PC World also reported its biggest-ever start to Black Friday with eight sales per second and 30 TVs per minute selling online.

Guy Anker, managing editor of Moneysavingexpert.com, said: "The benefit of shopping online is it's so much easier to compare deals with a few clicks so they know whether the price after that 20% discount really is the cheapest on the market.

"Let's also remember today is a working day, with millions on office computers or on their smartphones at work able to shop easily and quickly online."

But on the high street and in supermarkets there were no signs of the huge crowds which gathered last year, or the scuffles which broke out as customers fought over big-ticket items.

The Boots flagship store on Sedley Place, central London, was one of a handful of shops which opened extra early, advertising deals on huge posters by the shop entrance.