National Australia Bank has apologised to customers as some services recover from widespread outages.
The big four bank confirmed it was experiencing technical issues on Monday.
NAB's mobile banking app, desktop internet banking, merchant terminal and trade services have been impacted by the outage.
"We're really sorry for the impact this is having," the bank tweeted.
"We know this is not how anyone wants to start their Monday and we're working to fix it as soon as possible."
All major Australian cities have been hit by the problems, an outage map shows.
Bank customers are still able to use ATMs, NAB cards and Apple Pay.
In a statement to AAP, NAB said some services are now coming back online including NAB Trade, NAB Connect and NAB Merchant terminals.
Customers are advised to check for further updates on NAB's outage webpage and social media.
