Electronic payments at retailers, including Woolworths, as well as many services across the banking system were hit by a Telstra outage on Thursday afternoon.
The supermarket giant said a Telstra network issue meant its stores had to process payments manually, with some accepting cash only.
However, at 5:45pm (AEST) Woolworths said Telstra had advised the network connection was back up and running.
"We expect our systems to come back online and resume normal service through check-outs over the next hour," a Woolworths spokesperson said.
"We apologise to customers for the inconvenience and delays in shopping this afternoon."
Service station chain Caltex was another company that tweeted its EFTPOS systems were down, but the ABC understands the issue was widespread, also affecting some HICAPS medical claims and payments services.
The Commonwealth Bank has confirmed that an issue with one of its telco providers affected ATMs, EFTPOS, some in-branch services and CommSec log-ins on Thursday afternoon.
However, CBA customers reported that at least some ATMs were working at 5:30pm.
Westpac said it was aware that some branches, ATMs and services in the Sydney metro region were not working because of a broader network failure in the region.
NAB confirmed it was also experiencing technical issues with some of its electronic payments services.
ANZ also confirmed via its official Twitter account that many customers were experiencing problems using EFTPOS.
"We can confirm there is a widespread issue with EFTPOS terminals in Australia. This does not appear to be isolated with ANZ, however we are working to have this resolved on our end as soon as possible."
The ABC understands that the problem relates to a payments processing network operated by Telstra and affects all banks in some way.
The system handles low value transactions and some property settlements, however the systems responsible for major transactions between financial institutions are unaffected.
Australia Post has also reported widespread problems with many of its banking and payment services.
"We're currently experiencing software issues in retail and urgently seeking a fix," it tweeted.
"EFT payments over $100 & Agency payments over $200, Bank@Post withdrawals, deposits and balance enquiries are affected. Commbank withdrawals under $100 and deposits of any kind are unaffected."
NSW Ambulance experienced technical difficulties it believes were connected to the Telstra outage, but said triple-0 calls were unaffected.
"NSW Ambulance and E-Health are working with Telstra to manage and resolve the issue," a spokesperson said.
Telstra working to identify problem as service restored
At 5.50pm (AEST) Telstra said its services were beginning to be restored.
"We continue to investigate the issue affecting data services, including EFTPOS and access to ATMS, for a number of enterprise customers nationally. Many of our services are starting to restore," a Telstra spokesperson said.
"We're sorry for any issues caused and will provide an update when we know more."
Telstra has confirmed it is a national issue and said the fault started some time between 3-4pm (AEST) and was identified by the company.
