A Telstra outage that caused headaches for shoppers and bank customers around the country has been blamed on an "unusually large volume of traffic" in NSW.
The nation's big four banks and major supermarkets were among those caught out in the failure, which affected some EFTPOS terminals and access to ATMs on Thursday.
"We are continuing to investigate the exact cause of this issue, but early investigations suggest it was caused by an unusually large volume of traffic across network links in NSW," Telstra said in a statement on Friday.
It took the telco giant hours to fix the problem.
"We apologise for the interruption to some data services yesterday afternoon. We know how frustrating this was and worked to restore them as quickly as possible," it said.
All services have now been fully restored, Telstra said.
Commonwealth Bank had issues with some of its merchant payment terminals which left some retailers unable to accept card payments during the outage.
"Services have returned to normal including our ATMs. We apologise and thank you for your patience today as we worked to restore services," the CBA tweeted.
Australia Post, St George Bank, NAB, Westpac and ANZ were also impacted.
"All EFTPOS transactions, bill payments and banking services are back up and running. Thanks everyone for your patience and understanding," the postal service tweeted.
Westpac tweeted on Thursday night that the majority of branches, ATMs and services impacted were "back up and running", before thanking customers for their patience.
Caltex service stations, Coles and Woolworths stores, Big W and liquor retailers BWS and Dan Murphy's weren't spared from the outage.
"Telstra has advised us the network connection is back up and running," Woolworths told AAP, offering an apology to customers for the delay.
