Westpac says processing of payments to other banks has been completed after a technical problem overnight.
Westpac spokesman Chris Mirams said all affected automated payments would be honoured and no affected customers would be left out of pocket as a result of the fault.
Online banking, eftpos, ATMs and branch banking services were all available, he said.
The fault affected payments, including some salary payments, and Westpac's transactions with other banks.
Westpac said in an earlier statement that the problem was being urgently investigated.
"We appreciate the severity of this situation, and regret the inconvenience this will cause affected customers,'' the bank said.
Any fees, charges or interest occurring as a result of the fault would be reversed, it said.
The bank urged customers not to try to reprocess any affected transactions, and said they would be processed once the issue was resolved.
