SkyCity is apologising for failing to intervene with a repeat player in Auckland.

A customer complained to Internal Affairs after gambling went continuously unnoticed on 23 occasions.

SkyCity says a system failure meant they went undetected - and it's committed to improving its harm minimisation technology.

Chief Operating Officer Callum Mallett says they'll close the casino for five days to work with the Department of Internal Affairs on how to improve.

"We have an obligation at the five-hour mark to ensure that we have interactions with a customer, and we failed to do that. We're sorry for that, and we are focused on doing better."

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