The Commonwealth Bank is working to restore services and identify the cause of technical problems that have resulted in the bank suffering its second major outage in a week.
The bank has been struggling with service degradation since it performed standard quarterly system upgrades over the weekend.
Major problems with access to services started on Sunday and continued into Monday.
Customers reported widespread issues accessing accounts in CBA's online NetBank platform and CommBank mobile application.
They reported being unable to make payments, access certain accounts and retrieve personal information. Others said they were unable to make payments at point of sale terminals.
Just before 5pm on Monday the bank advised it had restored services. However, a smaller number of customers continued to report issues throughout the week.
A second major outage hit users late last night, with many customers taking to social media to report the same problems accessing NetBank and the CBA app others had been experiencing throughout the week.
iTnews understands the bank has been rolling back upgrades performed over the weekend to identify where the problem lies, and has isolated the area in which the issue resides.
It is currently unable to provide a time of restoration, and declined to comment on the specific nature of the issue.
In a statement the bank advised its planned updates were "taking a little longer than we hoped".
"The cause of the problem is under urgent investigation and we are working to have full services restored as a matter of priority," a spokesperson said.
"We apologise for the inconvenience to customers and thank them for their patience."
Update 10:45am: CBA said services were returning to normal.