Commonwealth Bank says things are on the mend following "intermittent issues" some customers have experienced across its services.
"We can confirm we have identified the cause of the issue and services are being restored," it said in a statement issued late on Monday afternoon.
"We are very sorry for the inconvenience this has caused.
"We know how much customers depend on us and sincerely apologise to those who have been impacted today."
Australia's biggest bank said earlier in the day its call centres were experiencing higher volumes of customer enquiries and longer wait times due to problems affecting online banking, payments and merchant terminals.
The bank said it was urgently investigating the issue and its branches were open but staff there would not have further details.
According to outage website DownDetector, almost 3500 customers were reporting issues across the country mid morning.
However that number had dropped below a thousand by early afternoon and was fewer than 150 by 5pm.
The bank said customers should note that there may be delays in some payments as it continued to bring services back online on Monday evening.
Australian Associated Press
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