NAB's chief customer officer of Consumer Banking and Wealth Andrew Hagger confirmed the outage, saying it was also affecting NAB merchant terminals and its health claims and payments system (HICAPS), which is a payment solution for health care providers.
NAB experienced a number of system outages last Tuesday night, which were still affecting services such as mobile internet banking and customer call centres the day after.
At the time, Hagger apologised on behalf of the bank, confirming that the outages resulted in a delay in processing some transactions.
"Our team remains vigilant and continues to monitor system performance, to safeguard against further interruptions," Hagger said, after services were restored late Wednesday.
"We are working with customers on a case-by-case basis to ensure none are left out of pocket as a direct result of this outage."
Updated 12.10pm AEST: Added commentary from NAB spokesperson.