ASB says problems with its electronic banking services which potentially affected thousands of customers on Sunday have been fixed.
Customers experienced problems from early in the morning with ATM, eftpos and internet banking services following computer maintenance overnight on Saturday.
The banking problems also meant limits on bank card withdrawals.
ASB chief operations officer Russell Jones says although the problems have been fixed, technicians will be on stand-by overnight on Sunday to monitor the system.
Mr Jones says the bank will compensate anyone left out of pocket due to the faults.
He would not be drawn on what caused the technical problems, but confirmed it was not the result of any sort of computer hacking.