ANZ New Zealand says it will remain vigilant this week for any potential problems after a relatively-untroubled merging of its ANZ and National IT systems.
Over the weekend, the bank shifted 2.6 million ANZ accounts and customer records to National Bank's IT system.
ANZ spent $221 million merging the two and carried out four dress rehearsals to prove the data could be converted correctly.
Chief operating officer Craig Sims is relieved the shift went relatively smoothly, but says the bank is keeping a close eye on it just in case.
Mr Sims said customers now log into an ANZ-branded online banking website.
The bank's next major task is to rebrand National Bank branches to the corporate blue of ANZ over the next two years.