Hundreds of people formed a queue outside the Next store in the Silverburn centre in Glasgow three hours before it opened at 6am.
It comes after reports that £350 million was spent online in the UK during Christmas Day.
Some stores have cut prices by 80% in order to attract shoppers, and retailers believe it could be the busiest Boxing Day ever.
Silverburn's deputy manager George Reader said: "It's been nothing short of incredible, we've had people arriving at the centre since just before 3am this morning, which we've never seen before.
"Normally the Boxing Day sales are associated with clothes but people have been buying homeware, gadgets, phones, everything, people are still coming in and buying toys. What we're finding is people who were given cash or gift vouchers as presents are all out today to make the most of the deals."
The Glasgow shopping centre enjoyed a 20% year-on-year boost in footfall in the week leading up to Christmas.
Mr Reader believes people still like to have a look around shops despite the continuing growth in online purchases.
"The internet and online buying is definitely there, but the nation's favourite hobby is retail shopping and they love to get in and out of different shops as shown today, and we're expecting this to be our busiest Boxing Day as well."
Shoppers also had an early start at Braehead in Renfrewshire and Union Square in Aberdeen, queuing from 5am.
Union Square experienced a 9% increase in shopper numbers in the three days before Christmas compared to last year.
Braehead manager Gary Turnbull said: "The early birds were out again this year at the crack of dawn aiming to catch a bargain at our stores and more than a thousand people were queuing from as early as 5am for the Next sale to start at 6am.
"Some people had even brought along folding camping chairs to sit on while they were queuing and had flasks of tea and coffee to keep them going.
"The tradition of hitting the shops on Boxing Day is now almost as much part of Christmas as Santa, roast turkey and all the trimmings."
City centres were busy throughout the day and the EK centre in East Kilbride was another hot spot despite many shops starting sales before Christmas.
Centre director Ian McLelland said: "Boxing Day has proved yet again to be one of the busiest shopping days of the year in East Kilbride.
"We sold a significant number of EK gift cards over the festive season and judging from the crowds, it looks like many of these have reappeared in Christmas stockings across the region."