CommBank has reported that some customers may be experiencing issues with its systems including NetBank.
“We’re working to resolve this and apologise to affected customers,” tweeted the bank this afternoon.
“We're aware of the issue and are working to restore service as quickly as possible,” read a note on the NetBank page.
Unhappy customers have taken to social media to vent their frustration
One customer left a comment on the bank’s Facebook page which read “Good to see the profits have been used to sort these issues out. Standard.”
A CBA spokesman said the cause of the problem is under urgent investigation and it is working to have full services restored.
"We apologise for the inconvenience to customers and thank them for their patience."
In June, CBA experienced a similar outage which affected its Eftpos machines and access to its online banking system NetBank.
The outage meant some customers couldn’t pay for purchases at CBA Eftpos terminals or access NetBank accounts.
Follow Hamish Barwick on Twitter: @HamishBarwick