The Commonwealth Bank says an outage led to customers being unable to access its banking services for much of Tuesday.
Some customers complained online about not being able to access their accounts or pay for items, explaining they had to look around for loose change or leave stores unable to pay for groceries.
The bank confirmed the outages at 11:45am, and a bank spokesperson said services were returning to normal at about 1:45pm.
The bank apologised and it said some customers would continue to experience delays.
"Our services are beginning to return to normal however some customers may be experiencing a delay with payment transfers," the bank said.
"We apologise for any inconvenience this has caused and appreciate your patience."
By 5:30pm the bank said services had returned to normal.
It said anyone having trouble using the CommBank app should "uninstall and re-install, as this will solve the majority of issues".
The bank did not detail the cause of the outage in its statements online.
Last month, customers experienced technical issues with the Commonwealth's NetBank and the CommBank app.
In the same week, merchant terminals and online banking went down.
