More than 10 million Australians were cut off from internet and phone services on Wednesday after unexplained outages struck one of the country's largest communications companies.
The mystery glitch crashed electronic payment systems, disrupted phone lines used by ambulances and police, and briefly halted rush-hour trains in the southern city of Melbourne.
Optus, a subsidiary of Singapore telecommunications company Singtel, said it had restored services on Wednesday evening -- but it was unable to pinpoint what had caused the fault.
A "technical network outage" detected at about 4:05 am Sydney time had cut off customers, Optus chief executive Kelly Bayer Rosmarin told national broadcaster ABC.
"We are very sorry that this occurred and I am happy to say that services are now restored again," she said.
"Until we have done a full, thorough root cause analysis we really can't provide more information," she said, describing the outage as a "very rare occurrence".
The Optus boss said there was "no indication" the issues were the result of hacking.
Just over a year ago, more than nine million Optus customers had their personal data stolen in a cyber attack.
A host of organisations and businesses confirmed their connections had been restored, including the federal department of education, the Royal Melbourne Hospital, and Australia's Commonwealth Bank.
Optus, Australia's second-largest telecoms firm with more than 10 million customers, had struggled through the day to bring its systems back up.
- 'Absolute disgrace' -
Dozens of hospitals were unable to receive phone calls during the outage and landline phones on the Optus network could not ring emergency services.
The poisons hotline in New South Wales state also said it was impacted.
And there was morning rush-hour chaos in Melbourne after what officials described as a "communications outage" disrupted train services.
Australian Communications Minister Michelle Rowland said the Optus outage had been caused by a "deep fault" in a "fundamental" part of the company's network.
"What we do know is that this is a deep fault. It has occurred deep within the network," she told reporters.
"It has wide ramifications across mobile, fixed, and broadband services for Optus customers.
"Customers are clearly frustrated about it, and Optus should respond to that accordingly."
Australia's Communication Workers Union said the outage was an "absolute disgrace", linking it to recent job losses at the company.
- 'Borrow a phone' -
Royal Melbourne Institute of Technology researcher Mark Gregory said the disruptions showed there were fundamental problems in Australia's communications networks.
"Single point of failure related outages have occurred too often over the past decades and it is time that the government steps in to force the telecommunications industry to build redundancy into the networks and systems," he said.
Ramsay Health Care said on Facebook that the outage took down phones at its 73 private hospitals and day surgery units, while Sydney's Westmead Private Hospital also said its phone lines were affected.
A carer said he had not been able to call an ambulance for one of his patients, telling ABC Radio Melbourne: "I had to run out on the street and borrow a phone from someone walking his dog."
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