Customers attempting to log into the CBA service on Thursday are being greeted with an "important message from NetBank", which states that some customers are being affected by the problem and services should be resumed later this afternoon.
A Commonwealth Bank spokesperson told ZDNet Australia that around half of NetBank's customers are affected.
"We have had some problems with NetBank this morning. Technical difficulties resulted in just over 50 percent of users trying to log on being unable to access the site. We expect that the site will be fully accessible mid afternoon," the spokesperson said.
The service was still unavailable at lunchtime on Thursday.
This is just the latest in a series of embarrassing problems at Netbank, which spent AU$100 million to upgrade its systems four months ago.
The project had its fair share of glitches even in the pilot stages where users of the service complained that they were not given any notice that their service had been upgraded.
Within days of the launch, some more users experienced problems as the bank switched over to its new system.
Last month, Netbank was down for most of a business day after another unexplained glitch.