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Optus, Australia's second-largest telecoms firm with more than 10 million customers, said it had identified the outage at around 4:05 am local time. Image Credit: AFP

Sydney: 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 country's largest city, Melbourne.

Optus, a subsidiary of Singapore telecommunications company Singtel, said "some" services had been restored on Wednesday afternoon - but it was unable to pinpoint what had caused the fault.

"Our team is still pursuing every possible avenue. We had a number of hypotheses and each one so far that we've tested and put in place new actions for has not resolved the fundamental issue," company chief executive Kelly Bayer Rosmarin told national broadcaster ABC.

"When we have identified a root cause and a time for restoration, we'll be updating everybody as soon as we can."

She said there was "no indication" the outage was the result of hacking. Just over a year ago, more than nine million Optus customers had their personal data stolen in a cyberattack.

In a separate statement, the company said it "may take a few hours for all services to come back on line".

The Australian government said mobile phones, landlines and broadband internet had been impacted.

Optus, Australia's second-largest telecoms firm with more than 10 million customers, said it had identified the outage at around 4:05 am local time.

For the next nine hours, widespread issues plagued Optus networks as engineers scrambled to find a fix.

'Absolute disgrace'

Dozens of hospitals were unable to receive phone calls, and landline phones on the Optus network could not ring emergency services.

The poisons hotline in the state of New South Wales also said it was impacted.

And there was rush-hour chaos in Melbourne after a "communications outage" disrupted train services.

"I'm looking forward to Optus resolving this technical issue," Metro Trains Melbourne chief executive Raymond O'Flaherty said on Wednesday afternoon.

"We need to have our backup contingency arrangements in place and I'm hoping they'll solve their issues as soon as possible."

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."

Ramsay Health Care said on Facebook that phones were down at its 73 private hospitals and day surgery units, while Sydney's Westmead Private Hospital also said its phone lines were down.

Other companies to report issues included health insurer Bupa, airline Virgin Australia, and health and safety watchdog WorkSafe.

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."