The National Retailers Association is forecasting $5.6 billion in sales over the weekend, eight per cent higher than last year's discount sales event.

Of this, $2 billion is expected to be spent on online sales.

"Each year shoppers further embrace Black Friday and descend on shopping centres to cash in on bargain sales," NRA CEO Dominique Lamb said.

"CBD shopping precincts have endured significant drops in foot traffic throughout the pandemic, so we really encourage consumers to head into their respective towns and support these businesses."

The Australian Retailers Association also predicted sales worth $5.4 billion.

The four-day shopping period, from November 26-29, originated in the US to tie in with its Thanksgiving holiday and has becoming increasingly popular in Australia as people shop early for Christmas.

An analysis by National Australia Bank estimates almost a million dollars a minute will be spent during the shopping frenzy.

Computers, appliances, games, toys, clothing and cosmetics are forecast to be among the most popular purchases, based on data analysing previous years' spending trends.

"One in six of all November retail sales happened during this four-day period last year and we're anticipating similar trends this year as the economic bounce back continues," NAB group executive personal banking, Rachel Slade said.

The Commonwealth Bank of Australia also notes from merchant data that sales during the 2020 four-day Black Friday sales period were 10 per cent higher than in 2019, boding well for the 2021 effort.

"Shoppers across the country are increasingly taking advantage of the recent move towards pre-Christmas discounting and we would expect this trend to continue this year," CBA's head of consumer and diversified industries, Jerry Macey said.

NAB expects online and physical cash tills to ring up $5.5 billion around the country, with NSW setting the pace with a $1.74 billion splurge, followed by Victoria laying out $1.45 billion and Queensland spending $1.12 billon.

Australia Post is also gearing up for a frantic weekend as savvy shoppers take full advantage of the online sales and get their Christmas presents sorted in plenty of time before recommended last sending dates.

"We know people are keeping a close eye on the big online sales events and planning ahead for what they want to buy, so we're expecting this year to be huge," Australia Post's Gary Starr said.

However, financial comparison website RateCity.com.au issued a note of warning to shoppers, urging them not to get too carried away.

"Sale events such as Black Friday and Cyber Monday are marketing stunts designed to get you spending," RateCity research director Sally Tindall said.

"These events typically have a deadline on them to encourage people to buy on impulse, potentially without thinking through the purchase or doing a price comparison."

Australian Associated Press