Kiwibank says it has restored its systems and is now processing incoming and outgoing transactions.
A technical problem threw its services into chaos earlier today and it was racing to resolve issues before the critical time of midnight.
The bank expects all ingoing and outgoing transactions to be completed by midnight, spokesman Bruce Thompson said.
Customers will progressively be able to access accounts via the internet and phone banking, but there could be some overloading for short periods over the next few hours as people swamp the system.
ATM and Eftpos services are operating and incoming payments are being credited to accounts and available.
Mr Thompson said there had been problems with the core banking system throughout the day.
That had affected the bank's ability to process transactions, and the ability of its customers to get access to their accounts through phone banking and the internet.
While ATM and eftpos transactions had worked through the day, an issue also developed with those services this evening, Thompson said.
The result was that when people tried to use ATM or eftpos those services only worked on the amount of available funds in people's accounts as at 6pm.
The critical time for the bank was midnight.
If the systems were not operating fully by then, there would be significant difficulties processing transactions from other banks that could include wages, salaries and benefits.
Customers were venting their frustration on Facebook, with one saying he had been trying to gain access to his account since 10am, another saying her family had not yet had dinner, and others worried they would not be able to make automatic payments.
Several complained about a lack of information from Kiwibank.
Bank staff would tomorrow look at what caused the two outages between 3.45pm and 4pm and 6pm and 11pm.
"What had concerned us were the transactions between the banks. If we weren't up and operating ... it would have been chaos tomorrow, but we got there."
- The Dominion Post
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