National Australia Bank on Saturday suffered what it described as a "nationwide outage" to some of its technology systems, leaving customers unable to access banking services or withdraw money.
Customers took to social media to vent their frustrations, with some saying they were left unable to pay for groceries or refuel their cars.
“Loyal member for 15 years and you leave me standing at the supermarket altar with a trolley full of shopping," said one Twitter user.
The bank tweeted just after midday on Saturday that some services were coming back online.
“We're sorry and it's not good enough ... but we'll get it fixed as soon as possible," NAB chief customer officer business and private banking, Anthony Healy, said in a video posted on Twitter.
NAB is one of Australia's four largest retail banks with a customer base of nine million, according to its website.
“Every single day we work on our technology to ensure we can provide reliability to our customers,” said Cindy Batchelor, executive general manager of NAB Business, when addressing the media over the weekend.
“So, we’ll get underneath root cause. There is always a review of an incident like this – but as I said, every single day, we strive to provide that reliability and we will continue to do that.”
According to Batchelor, the outage was a result of a “systems failure”, citing a “power issue” as the root cause of the damage, while also insisting that “no personal data has been compromised”.
“Every customer has the opportunity to come and talk to us about the impact they’ve had specifically on their business,” added Batchelor, when quizzed about possible compensation for businesses impacted.
“And our intention is to work with each and every one of them to make sure they have no financial loss associated with the outage today.”
The outage follows growing customer discontent with the so-called "Big Four" banks, which have suffered numerous embarrassing disclosures at an inquiry into financial sector misconduct.
A spokesman from the bank told Reuters by telephone that it was a national outage, without elaborating on its cause.
The Bank of New Zealand, a NAB subsidiary, also experienced outages on Saturday across New Zealand, but the spokesman was unable to confirm a connection between the two incidents.
(Reporting by Will Ziebell in Melbourne; Editing by Joseph Radford)