"It will be welcome news to retailers, keen to stem spending attrition from the local economy."
However, BNZ said it was cautious "to read too much into the low growth rate for international purchases".
BNZ director of institutional research Gary Baker said he expected growth rates for international purchases to recover to recent norms in January and February.
"What makes me think that it might recover to a normal level and that December is a bit of a blip is the November numbers for international purchases were very strong," Baker said.
"[Spending on] electronic goods were up over 30 per cent on the previous November and they are quite big categories for people buying online - electronics, clothing and books."
Traditional spending volumes in December could have been bought forward by the timing of new phone, game and consumer tech releases, Baker said.
"Given that we had a really a big, strong electronic spend component in November, I'm not surprised to see a bit of a drop in December."
Wilkinson said growth in local online spending could be attributed to consumers being more aware of the challenges of buying products overseas.
"Shipping delays and the chance these will be subject to duty are increasingly weighing on shoppers' minds. In some cases the price differential is not that great, so there's some shifting perspectives in the way people determine their purchasing destinations now."
Consumers had started their Christmas shopping earlier than normal last year, likely driven by promotions and consistent weather, Wilkinson said.
"Appliances and the food sector were clear winners this Christmas. Some categories, such as clothing, have struggled as shoppers prioritise spending toward home and 'nesting' products."