Westpac has resolved an issue which prompted anger from customers as access to funds were locked and account balances showed zero.
Downdetector, a website that logs internet outages, had more than 100 reports on the bank by 6.30pm on Friday.
At the time, the bank said it was aware of the problem and working to fix it as soon as possible.
One man, who did not want to be named, said he had just arrived from Australia and was shocked when he and his wife's debit cards all declined when they tried to use them at the airport.
"None of my cards would operate but, I checked my bank account details online, everything was saying zero. It looked as though it had been wiped out," he said.
Another woman came home from a dinner out in tears after having all her cards declined.
Numerous comments on Westpac's Facebook page had shared similar experiences on Friday night.
More than 12 hours later, the bank's Facebook posts wishing customers a happy Lunar New Year were pulled after comments criticising the bank's lack of updates on the problems affecting customers.
Replying to frustated comments on its social media page, the bank said it was "really sorry".
"It's not fraud, it's a technical issue in which people's accounts are showing as zero balance.
"We're working hard to fix this. Sorry again!"
Shortly before 8am, the bank advised the situation had been resolved and apologised to all affected customers.
In a statement, a spokesperson for the bank said they apologise to the customers who were affected.
"Our tech teams implemented a fix overnight and all accounts were restored and are back functioning as normal. Work is underway to identify and remediate any residual issues," they said.
One customer, who did not want to be named, said they were unimpressed by the bank's response to the fault.
The customer said it took three attempts to speak to a bank representative when duplicate transactions started appearing on their account on Friday.
Meanwhile, a banking expert said the country's reliance on electronic transactions made breakdowns in banking systems incredibly disruptive.
Massey University associate professor Claire Matthews said there were alternative options to ensure a person was not stuck without money if their bank had issues.
"If you've got some cash, then you've got an alternative means to making some payments.
"That may not be terribly helpful, because you're not necessarily going to want to hold a lot of cash, but having access to perhaps another bank, so you don't have all your money in one spot, credit cards are obviously another payment option."
Banks were obligated to fix problems as quickly as possible and assist customers within reasonable grounds, she said.