Several hundred people were waiting outside Myer's Sydney store when doors opened at 5am on Tuesday, with one group arriving on Christmas afternoon to be first in line.
At the head of the line, Kiram Redey and his friends arrived just after 5pm on Christmas Day.
"This is the first time we've come here," Mr Redey told AAP.
"We are so excited."
Australian shoppers are expected to spend about $2.4 billion on Boxing Day, according to the Australian Retailers Association.
The ARA has forecast Australians will spend almost $16 billion between Boxing Day and January 15, up almost 3 per cent on last year.
NSW shoppers are expected to spend most at the post-Christmas sales. It's predicted they'll splurge $766 million, just a touch more than Victorian bargain-hunters.
ARA executive director Russell Zimmerman said with global giants entering the Australia market, local retailers were working hard to appeal to local customers.
"As convenience is key for today's consumers, retailers who have ensured their physical stores are accurately staffed will not only thrive today but see further growth in the new year," Mr Zimmerman said in a statement.
The newly-launched Amazon Australia, however, hopes to divert customers away from traditional brick and mortar stores by offering online sales from midnight on Tuesday.
The online giant, which opened earlier this month, will be spruiking hundreds of deals across all categories, including fashion, books, movies and music.
ARA's executive director Russell Zimmerman says the online sector will be a driving force behind this, as well as food and hospitality spending.
"Many food retailers will be discounting their fresh produce post-Christmas for families spending time at home during the holidays," he said.
Myer and David Jones opened their doors at 5am at the major CBD stores in Melbourne and Sydney to kick off their stocktake sales periods.
Myer expects more than 1.6 million customers around Australia on the first day of the sales, and make more than 600,000 individual transactions.
David Jones also expects more than a million customers to pass through their stores and says a further one million are likely to browse through the sales online.
JB Hifi is also preparing for customers to swarm their stores to take advantage of discounts on cameras, laptops, TVs, phones and other electronics.
