Greg McKenna, chair of the Police Bank and a Business Insider Australia contributor, has speculated that a Telstra outage might be an underlying cause of the disruption.
Telstra has also since tweeted a confirmation.
CBA, Westpac, ANZ and NAB all hit.
For the red and black bank, the outage has seen terminals across New South Wales impacted, and parts of Queensland affected.
"We are aware of an issue affecting some of our services".
'How can we rely on your services when all our cards are declined?
The latest problem comes just weeks after the Reserve Bank of Australia revealed that outages had soared by 40 percent and warned banks and telcos about the dangers of ageing infrastructure. "We apologise for the inconvenience and thank our customers for their patience", a Woolworths spokesperson said.
Commonwealth Bank customers first reported issues earlier this afternoon with ATMs and EFPTOS.
The Telstra network outage may affect people attempting to use EFTPOS machines, where they are presented with an error code x8.
"We can confirm the CommBank app and NetBank are still working".
The problems at this stage do not appear to be affecting all customers, with a Sydney CBD fringe Hicaps user telling iTnews services were working normally.
Westpac said some Sydney machines and branches were "non-operational", but customers on Facebook claimed they were experiencing issues in Melbourne and Brisbane also.
"The cause of the problem is under urgent investigation and we are working to have full services restored as a matter of priority", CommBank said.
The outage is also having a crippling impact on the nation's fast food industry.
According to the ABC, the issue relates to a payment processing network operated by Telstra, which has impacted all banks in some way. "We're working closely with Telstra to rectify the issue as quickly as possible". "Internet and mobile banking services remain available for customers during this time", a Westpac spokesperson said in an email to Gizmodo Australia.
A subsequent tweet from ANZ's official handle at 4:31pm clarified that the issue is "wide-spread".
We'll be updating this story as we learn more.