Aussies are spending as much as 1 billion a day for the duration of the Christmas period.

The Australian National Retailers Association (ANRA) predicted sales amounting to $29.6 billion with the last minute shoppers most likely to spend an additional $61 million online on Monday on gift vouchers.

In the early parts of the Christmas period, Aussies were spending on electronics, furniture, homewares and books. As Christmas day drew to a close come Monday and Tuesday, spending are predicted to switch to presents, clothes, food and alcohol.

"We're certainly in the space of Australians, overall, spending well over a billion dollars a day over the weekend," National Retailers Association (NRA) chief executive Trevor Evans told AAP on Monday.

Mr Evans said that the spending wil increase up until Boxing Day.

"The fact that they're doing that before Christmas indicates that the sales are going to be very genuine and very big indeed come Boxing Day when it comes down to a clearance of stock situation," Mr Evans added.

Chief Executive Margy Osmond, on the other hand told AAP that shoppers were cramming for gift cards, thus, increasing their spending with their online purchase.

"People like to get the gift cards because they can use them in the post-Christmas sales and get an extra bargain.This is the first Christmas where retailers are engaging in a much more personalised way with shoppers in terms of the sale activity. We'll see an extra sophistication of that into the Boxing Day and post-Christmas sales." Ms Osmond said.

Meanwhile, shoppers in West Australia spend over $3.5 billion on Sunday for the pre-Christmas extended trading hours. About $3.5 billion is expected to be spent in WA, according to ANRA. West Australians were the nation's highest spending last-minute shoppers, and were forecast to have shelled out $168 each over the past two days alone.

WA shoppers still prefer to buy gifts from local shopping centres after conducting research online.

"The centres were open from 8am and it was busy from the get go. It is early days but we are certainly seeing a lot of happy customers, customers are voting with their feet. Centres offer you what you can't get online. You can get your nails or your hair done, meet for lunch and socialize," Westfield regional manager Malcolm Reed told The West Australian.