"Online banking balances and transactions are also not currently showing for credit cards. We're working hard and fast to fix the problem and will let you know as soon as it's resolved. We apologise sincerely for any inconvenience caused by this technical issue," it said.
"You can also see your credit card balances and transactions online. We understand how frustrating technical outages can be and are sorry if this affected you."
Carolyn, from South Waikato, said she had been at a checkout in Countdown around 5pm today buying meat for dinner when her card was declined.
She had cash so was able to pay for the food, but she was embarrassed and "stressed out" at being declined.
"Whether you've got the money or not you still get looked at."
She said this had been the second time recently that she had been unable to use her BNZ card.
On Saturday, customers were also unable to log in to online banking services, which caught out hundreds of customers at supermarkets and other stores.
That outage was reported at 10.19am and was not resolved until about 3.20pm.
Many customers expressed their disappointment on social media.
"I've had two declined transactions on my debit card and it is incredibly embarrassing and inconvenient. I think you need to do something about it," one person wrote.
"Why are there so many issues? I thought these were fixed over the weekend," another asked.
