Customers are furious with BNZ after hours of trying and failing to use their mobile and online banking service.
The problems started early on Saturday morning and continued into the early evening, leaving customers without online hours for more than five hours.
One Herald reporter was able to access their mobile but not online banking about 5pm.
Many customers said on the bank's social media pages they felt outages for the mobile and online banking systems were too common.
"BNZ Mobile App down — again," wrote Jason Belworthy on Facebook.
"I have accounts with two other banks and have never experienced their Apps being down.
"What is going on at BNZ."
Another customer said the bank should change their motto to "Major Outage".
"Switching to ASB next week," one Twitter user threatened.
"Your network problems are too frequent. Couldn't pay for groceries. Embarrasing [sic]."
A social media administrator for the bank said online the team was working to fix the problem and actively monitoring the situation.
A BNZ spokeswoman said customers had been experiencing an intermittent issue which had been sporadic throughout the day. There hadn't been a blanket outage.
BNZ apologised for any inconvenience caused and said crews were continuing to work on the issue tonight.
The spokeswoman advised people who were experiencing problems to try logging out and logging in again after a few minutes.