Westpac is investigating the cause of a technical problem that has hit its new online and mobile banking platform, locking out customers since Wednesday afternoon, Australian time.
Customers trying to log into the service and pay urgent bills are bombarding the bank with questions on Twitter.
The bank has yet to provide any details on the problems or offer an update on when services might be restored, urging customers to instead call in or use the cash machine network.
The problems come amidst the roll-out of a new online and mobile banking from Fiserv, which made its debut in November last year.