Australia's Click Frenzy sales will provide a multimillion-dollar boost for the nation's retail sector, experts say.
But questions remain about whether IT infrastructure will survive the expected surge in online traffic.
And customers are being urged to watch out for con artists.
About one million shoppers are expected to take part in the 24-hour Click Frenzy event, which kicks off at 7pm (AEDT) on Tuesday.
The sale is a copy of America's Cyber Monday event on November 26 and involves some of Australia's largest retailers, including Myer, Dick Smith and Westfield.
Dr Sean Sands, from Monash University's Australian Centre for Retail Studies says the occasion will be worth "many, many millions" to the companies involved.
"I think there's been 20,000 to 30,000 people registering per day over the last week or so, so it's going to be a pretty big deal for retailers," he told AAP.
But with so many people expected to pile online at 7pm, there are concerns about the retailers' servers and access to some sites - particularly for mobile and tablet users.
"It's a bit of an unknown factor at the moment and a lot depends on how many people actually take part," Dr Sands added.
He said some of the retailers did not have mobile-specific websites, so some shoppers might not be able to see their offers.
In a message posted on the Click Frenzy website, organisers acknowledged that the site's servers could crash.
"We have taken every precaution to ensure our servers will not go down, and we have advised our retailers of the traffic volumes they should expect," it said.
Internet security software firm Bitdefender has warned Click Frenzy shoppers that con artists may try to take advantage of the sale by setting up fake websites or stealing credit card details.
The firm urged shoppers to avoid making purchases while connected to unprotected wi-fi networks and to avoid spoof websites.