Paymark chief executive Simon Tong said the results should be welcome news for retailers as they begin their final push for the last three full shopping days before Christmas.
''It's heartening to see the annual year-on-year growth rate building through December and climbing above the average for the year, which was around 3%.''
During the past seven days, spending was up 5.8% overall, making it one of the highest spending weeks of the year. On Thursday, Paymark broke through four million transactions in one day for only the sixth time in the company's history.
Figures supplied by Paymark showed that sales increased by 4.7% in the 21 days ending December 20.
Canterbury was up 6.4%, or $22.8 million, on the previous corresponding period; Otago was up 4.6%, or $7.3 million, and Southland was up 1.8%, or $1.4 million.
Total Canterbury sales in the 21 days were $379.4 million, Otago sales were $167.1 million and Southland $80.2 million.
New Zealanders look likely to be spending some time working on their homes and gardens this holiday season, with floor covering and furniture stores reporting spending growth of 20.6% on the previous period.
Garden stores and hardware/building supply stores were up 10.1% and 10.3% respectively.
Red Shed retailer The Warehouse has provided some top tips for Boxing Day shoppers, one of the busiest shopping days for Kiwis.
At the top of the list was: Make a budget. At times, sales can be overwhelming, especially when products are 40%, 50% or 60% off. Keep your budget in mind when shopping so you are not starting the new year on the back foot financially. If your budget allows, Boxing Day sales are a great opportunity to plan ahead and stock up on presents and family essentials for the rest of the year.
Look at the advertisements before the day: These are usually in newspapers on Christmas Eve. This way, you can make a note of what you are looking for and head to those departments first.
Wake up early: This tip might seem obvious but getting to the store early - or before it opens - can be the difference between getting that stand-out bargain and going home without the deal you are after.
Consider public transport: If it is possible to reach your shopping destination with public transport, make use of it. Not only is it better for the environment, you will also save time by not having to circle the car parks.
Consider grouping purchases: If you are short on time and just want to hit the beach, group your purchases by just shopping at one department store. Stores often bundle deals at this time of the year, another good way to make your dollars go further.
If you see something you like, buy it: Boxing Day sales are where you often do not have the opportunity to think on purchases or ask staff to hold them for you. If something catches your eye, and you like it, grab it.