An internal systems outage at Westpac took the bank's branch network offline around the country for about seven hours on Monday and forced teller staff to resort to manual processes.
At around 10:30am Monday customers began reporting being unable to access services in Westpac branches nationwide.
The technical issues only affected Westpac branches: online, phone, and EFTPOS banking all remain operational.
"We're just letting you know that some of our branches are experiencing issues with some of the applications that we use to handle in-branch transactions," Westpac said on its Facebook page.
It advised customers to process transactions either online or at ATMs instead of in branches.
"We sincerely apologise to customers for any inconvenience and will try and have our branches operating normally as soon as possible," a spokesperson said.
The systems lasted for around seven hours; at around 6pm the spokesperson said branch systems had been restored.
"Customers who have experienced a financial loss as a direct result of the branch systems issue will be compensated," they said.
It declined to comment on the cause of the outage, saying it was still investigating.
It's the second sigificant outage to hit the bank in three months following a glitch in late November that stopped online and mobile banking platforms from processing payments or showing correct balances for almost a week.
The project started late last year and is expected to take three years in total.