The country's four major banks said some of their transaction-handling machines in stores were not working.

Westpac Banking Corporation said on Twitter that some automatic teller machines in Sydney were down, while National Australia Bank Ltd and Commonwealth Bank of Australia also reported payment processing issues.

Australia and New Zealand Banking Group also said some of its point-of-sale payment machines weren't working.

The nation's biggest grocer, Woolworths Group Ltd, said cashiers were processing transactions manually.

A Reuters reporter at one supermarket in Sydney said the problem caused havoc as automated checkouts - which account for most checkouts at many stores - were shut down and staff checked customers' signatures to process card payments.

The country's biggest telecom provider, Telstra Corp Ltd , said it was investigating the issue and that a number of large customers were affected nationwide. It gave no further details on the nature of the problem.

The banks said that internet banking systems remained operational and that the outages were uneven.