Millions of Australians were left without mobile and internet after a network failure at telecoms firm Optus.
The failure caused transport delays, cut hospital phone lines, and shut down payment systems.
Optus, the country’s second-largest provider, said more than 10 million people and thousands of businesses were affected.
Services were restored after around 12 hours of disruption. Optus said there was no evidence of a cyber attack.
The firm blamed a “technical network fault” and said more time would be needed to investigate the root cause.
Wednesday’s disruption was reported around 04:00 (17:00 GMT). It took until around 18:00 for services to come back online.
Kelly Bayer Rosmarin, the company’s chief executive, said it had not yet identified what went wrong.
People across Australia were unable to call emergency services and critical helpline numbers, train services in the state of Victoria were also temporarily crippled.
The failures also affected other providers that use the Optus network, including Amaysim, Aussie Broadband, Moose Mobile, and more.