David Jones' attempt to hijack Australia’s first national online shopping event with a sale of its own has backfired, with the department store’s two week old website crashing this afternoon under the weight of heavy traffic.

A spokeswoman for the department store said unprecedented traffic to the site had caused the technical meltdown. By mid-afternoon, shoppers who earlier in the day had problems accessing some deals, could not even get on to the site.

"Basically, we've had an overwhelming response to our Christmas Frenzy event," the spokeswoman said. "Our stores have been trading well ahead of our expectations and our online site has been inundated with customers causing it to go into meltdown."

The site was inaccessible for about two hours. But it is now back online.

The department store which has previously been criticised for being slow to embrace online shopping had snubbed Australia's inaugural Click Frenzy event which begins at 7pm and has been touted as Australia's version of the American shopping phenomenon, Cyber Monday.

When organisers announced the 180-plus participating retailers last week, including Myer, Target, Dick Smith and online juggernauts The Iconic and StyleTread, David Jones was a glaring omission.

At the time, it said it preferred to observe the event before considering taking part in the future. Fairfax Media understands it also had concerns about whether the new website, developed by IBM could cope with the anticipated traffic.

Then Monday afternoon, on the eve of the Click Frenzy event, it announced it would hold a rival sale of its own – by no co-incidence, called Christmas Frenzy –  which was to run in store from 9.30am until 10pm today and online from 6am until midnight, with storewide discounts of up to 40 per cent.

A spokeswoman told Fairfax Media the event was timed to coincide with "competition activity".

This afternoon, she confirmed the in-store sale would continue until 10pm with online sales offered until midnight, once the website was restored.

Meanwhile, more than 180 retailers participating in Click Frenzy have been preparing their own websites to ensure they can cope with the heavy volume of anticipated traffic when the sale gets under way at 7pm.

Yesterday, Grant Arnott said a last-minute surge in pre-registrations - of 20,000 to 30,000 a day for the past week - meant he was now expecting well over a million shoppers to take part in the 24-hour event.

At 5pm today he confirmed they had now received more than 500,000 registrations with thousands more expected in the lead up to the sale.

Mr Arnott was forced to upgrade the Click Frenzy website to ensure it could cope with the volume of traffic and urged retailers to do the same.

"We've been working closely with our infrastructure company and we’ve been assured that the site will hold up," he said. "We're also passing the message on to our retailers that we’re revising up our traffic projections significantly."