Mr Collins said it was too early to say how the rest of summer would fare for Northland retailers but post-Christmas sales would keep turnover going.
Nationally, year-on-year spending increases during December were highest at appliance stores (up 10.3 per cent) and hardware stores (up 9.2 per cent).
Pet stores also enjoyed a 7.5 per cent surge in activity, with families welcoming new pets for Christmas or buying treats for existing furry friends.
The festive spirit was evident in a 7.1 per cent spending jump at cafes and restaurants, an 8 per cent jump at liquor retailers and a 6.3 per cent rise at department stores.
NZ Retailers Association chief executive John Albertson said December was in line with retailers' expectations. "Obviously retailers get reasonably optimistic ... you think that maybe this year will be better than expectations."
While retailers had passed the annual peak, the end of January brought with it summer season sales for clothing retailers and back-to-school trade.
Mr Albertson said while retailers were not predicting 2013 to be an easy year, there were signs the market was improving. December spending was up for the third month in a row.