The increase was due in part to the Shania Twain concert at Forsyth Barr Stadium giving a boost to Dunedin's retailers and hospitality industry.
The numbers come in Paymark spending figures for last weekend, released on Christmas Eve.
The Otago total came to $26.5 million, the region recording the second-largest increase in the country.
Palmerston North had the largest increase at 8.6%.
Spending was down in Gisborne, South Canterbury, the West Coast and Wairarapa.
Southland had an increase of 1.3%, and a total just short of $10 million.
Otago Chamber of Commerce chief executive Dougal McGowan said there were ''a number of reasons'' why Otago had returned such a good result.
That included the Shania Twain concert on Saturday night, attended by about 18,000 people.
The percentage increase was not usually as high as it was this year, and Mr McGowan said a growth in domestic tourism could also be behind the boom.
''Dunedin's sort of discovered itself.''
The Boxing Day sales were due to be ''just as big'' as the Christmas rush.
The spend per district rather than region was not available, but DowntownQT general manager Steve Wilde said it would be interesting to see the breakdown for Queenstown, because he thought the area had a ''soft'' season compared to the ''huge growth'' seen in the past five
or six years.
Increased numbers of people coming into the district had not translated to more sales at the till, as people dispersed around the wider Otago region, Mr Wilde said.
A statement from Paymark said retailers across the country were likely to be ''pleased but unexcited'' with the totals for the month of December.
''The running total for the first 23 days of December was up only 1% [excluding fuel] on last year.
''The biggest day spending-wise was Thursday, December 20 with $296 million (down slightly on the peak of 2017 which was $299 million on Friday, December 22), and overall spending in December is on track to hit $5 billion for the month, once Christmas Eve shopping is included.''
Nationwide spending on jewellery and watches was down last week from last year, but donations to charity had increased by 9%.
On December 22-23, spending on food and liquor was up 32% on the previous weekend at $130 million, as people stocked up.
At Dunedin's University Bookshop, general manager Phillippa Duffy said the shop had been busier than usual.
The bookshop's Jolabokaflod - late night shopping, inspired by the Icelandic tradition of getting new books out in the lead-up to Christmas and exchanging them on Christmas Eve - was introduced this year, and had been very well received by customers, she said.
Friday and Saturday before Christmas were traditionally the busiest time of the year for the bookshop.
''Fiction is always popular [as a gift],'' she said.
''Non-fiction has been increasing.''
