A number of National Australia Bank customers have been unable to access online and mobile banking this morning after the bank suffered what appears to a server error.
A bank spokesperson said NAB had been experiencing "intermittent" issues across both services since around 12:30pm today.
"We apologise to those customers who have been affected, and are working to restore full service as soon as possible,' he said.
"Customers can still visit a branch or use Telephone Banking to transact, or give us a call.
"We encourage all customers to keep an eye on social media for updates."
The bank declined to comment on the cause of the glitch. Users reported receiving an "IBM_HTTP Server Port 443" error when attempting to log in.
NAB is four years into a multibillion dollar, ten-year technology transformation to replace its legacy mainframe systems, developed in the 1950s.
The bank outsources the management of much of its IT infrastructure to IBM. It is currently in the midst of retooling core banking on an Oracle platform and consolidating several computer rooms down to two data centres, the latest being a new facility leased to it by Digital Realty.
NAB was forced to take its payments systems offline a few weeks ago after a technology glitch halted the processing of payments for around 12 hours. It did not reveal what caused that glitch.
The bank is the second of the big four in the past week to suffer an online banking outage.
Westpac’s online and mobile services were down for two days late last week. The bank was able to restore services on Thursday night but online and mobile banking went down again for a second full day on Friday.
It denied rumours of a distributed denial of service (DDoS) attack being behind the outage but is yet to provide the cause.
Westpac is preparing for the introduction of a new online and mobile banking platform, underpinned by Fiserv technology, to be launched in full by early next year. It has already delivered the first two of six releases for the new online platform.
Update 4:58pm: NAB confirmed services were up and running.