"We are working hard to get this issue fixed as soon as we can, and we apologise for any inconvenience caused."
BNZ's internet banking status page early this afternoon said some customers were unable to log in to internet banking, mobile banking and mobile business banking services.
The issues were affecting Apple and Android users.
It was the first outage recorded on the bank's status page since a major malfunction on the evening of July 2.
It was not immediately clear how many customers were affected today, or if the outage was connected to the new living costs payments.
The Government payment scheme totalled $350, split into three monthly payments starting today.
The payments were designed to help combat the impact of surging inflation on household budgets.
An estimated 2.1 million adult New Zealand tax residents earning less than $70,000 in the year to April are eligible for the payments.
People entitled to the winter energy payment who already received NZ superannuation or one of 10 qualifying benefits aren't eligible for the $350 payment.
Some Kiwis overseas have voiced surprise at being told they would also receive the payments today.
At one point, dead people would have been able to get the payment too, until the Herald approached Inland Revenue about that issue.
Today's payment is $116.67, as is the second one at the start of September. The third instalment for eligible people is $116.66, payable on October 3.