Argos has apologised to customers who were left frustrated when its website was offline for several hours on Sunday.

Shoppers were faced with 'crowd control' messages on the website during the outage, suggesting too many customers were trying to access the site.

The BBC reported it is believed to have been an internal fault affecting the website, but with less than 20 days until Black Friday, this raises concerns over the retailer's website capacity in the run up to peak trading.

Argos is running a number of promotions before Black Friday in an attempt to spread the load on its systems over several weeks rather than one day. It was running a 'three toys for the price of two' offer over the weekend which will run until tomorrow. Two further 'Red Friday' five-day sales events will occur before Black Friday on 27 November.

Last month, John Walden, CEO of Argos' parent company – Home Retail Group – said he was concerned over Christmas trading.

He said: "Trading at Argos during this year’s important Christmas season seems less predictable than usual, as both retailers and customers determine whether to repeat last year’s unusual Black Friday patterns."

Last week, H&M also struggled with website capacity as customers flooded the site in attempts to get their hands on the hotly anticipated collaboration with Balmain.

Customers were greeted with a landing page from H&M which stated the retailer was receiving a "lot of visitors on the site right now", due to "the high level of interest in our latest collection".

­­Meanwhile, at the end of last month, Marks & Spencer temporarily suspended its website after a technical glitch allowed customers to see each others' details when they logged into their accounts online.

Paul Heywood, managing director for EMEA at Internet performance company Dyn, said: "Downtime can cause huge problems for retailers. Not only does downtime halt sales, but the long term damage on a brand’s reputation can be immeasurable. Online retailers face high expectations from shoppers who expect the site to be secure, fast and reliable at all times and downtime means they turn to a competitor. To combat this, when an outage of magnitude occurs, retailers need to make sure that they have the right technology in place to still deliver an optimal customer experience."