Retailers in Canterbury lost more than $8 million in sales at the weekend after Saturday morning's quake.
Paymark, which processes 75% of electronic transactions, says total spending in Canterbury fell 32% on Saturday and Sunday, compared with the same weekend last year.
Sales across all retail sectors were badly affected. Sales on Saturday were down by nearly half, while trading on Sunday fell by a fifth.
Chief executive Simon Tong says some of the hardest hit were stores that normally would have experienced a rise in Fathers Day sales.
Electronics, camera and gift stores experienced a fall of almost 80% in sales at the weekend.
Canterbury retailers also experienced a tough month in August.
Mr Tong says Paymark is waiving its fees for businesses that have been unable to trade over the past few days, and is working with banks and telecommunications companies to get its customers operational again as soon as possible.