ANZ is the country's largest bank, and last reported an annual profit of $1.77 billion.

ANZ has breached the conditions of its banking registration, but will not be punished by the Reserve Bank.

The country's largest lender admitted the breach in its quarterly disclosure statement.

It said it had not included the Bonus Bonds Trust and ANZ PIE Fund in the risk-weighted exposures of its capital calculations.

The mistake had occurred due to failure to follow an internal process.

While in breach of the rules "for a period of time", the bank was now fully compliant.

ANZ spokesman Pete Barnao said the issue had first been disclosed in June, and the bank then brought it to the attention of the central bank.

"The Reserve Bank has acknowledged that the matter is not material, is highly technical in nature, and that no further action is warranted on the part of the RBNZ," he said.

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Banks that breach conditions of registration can face substantial fines, and in the worst-case scenario, have their licence cancelled.

However, the central bank has not issued a single penalty in the last 10 years.

Most of the breaches committed in recent years have been minor and technical in nature.

Last month, the state-owned Kiwibank was publicly told-off by the Reserve Bank over its failure to adhere to legislation which aims to counter terrorism financing.

The local branch of Chinese banking giant ICBC has managed to blot its copybook twice in the space of six months.

Chairman Don Brash, who is himself a former Reserve Bank governor, agreed it was not a good look.

Last year, ASB breached its conditions by temporarily overstepping low-equity mortgage restrictions.