A freak computer glitch at Australia's biggest bank froze cash machines and left millions of people struggling to access their money on Saturday.
National Australia Bank (NAB) said a corrupted file wiped out a huge number of transactions, including salary payments and transfers, and crashed some ATMs, angering many customers who were facing a weekend without money.
Spokeswoman Meaghan Telford said NAB was opening branches on Saturday and Sunday and bringing in extra call-centre staff as technicians scrambled to fix the problem.
"We're very apologetic," she told AFP. "We recognise this has caused people a lot of inconvenience. We're just working to resolve the problem."
Telford said the rogue file knocked out transactions on Wednesday, including salary deposits, bill payments and transfers to other banks, and then work to fix the problem hit Thursday and Friday's business.
As the electronic system buckled, some ATMs had crashed, she said, without revealing how many.
"There's been some issues with the electronic system because of the pressure the system has been under as a result of trying to resolve these issues," she said. "This has meant some ATMs have experienced issues."
Customers using microblogging site Twitter reported chaos with their bank accounts as mystifying sums appeared and disappeared, leaving many unable to withdraw cash.
Telford said NAB had cleared most of the delayed transactions but could not predict when the system would be back to normal. She did not estimate how many of NAB's 11.5 million customers were affected.
According to national news agency AAP, international banking giant HSBC's transactions to other banks, payroll deposits and direct debits were also affected, as NAB clears payments for HSBC in Australia.
NAB also warned on its website that its Internet banking was slow as millions of customers checked their accounts.
The meltdown comes at a time of growing discontent towards Australia's "big four" banks over rising interest rates and a swathe of minor fees, with even Prime Minister Julia Gillard urging unhappy customers to switch lenders.
Last week 250 investors brought a multi-million dollar lawsuit against NAB claiming it failed to properly disclose its exposure to toxic US debt during the financial crisis.