By Renju Jose and Praveen Menon
SYDNEY (Reuters) -Millions of Australians were left without a phone or internet connection on Wednesday after the country's second-largest telecommunications provider experienced an unexplained nationwide outage.
Optus, the Australian unit of telecoms firm Singapore Telecommunications, did not specify the reason for the outage or how long it would take to be restored. The networks have been down for more than 5 hours.
The telco has just over 10 million customers, about 40% of Australia's population.
"Our teams are working urgently to restore services. We will provide updates as soon as possible. We apologise sincerely to our customers," the company said on messaging platform X.
Optus was not immediately available for further comment.
The outage led to morning peak-hour chaos as train networks and ride share services were down briefly in some cities, while offices, cafes and other businesses grappled with disruptions to payment systems and other online operations.
Some have also said they are having trouble reaching banks and accessing banking services.
Commonwealth Bank, the country's biggest lender, said in a statement that some customers may encounter difficulties with some of its services. CBA said its call centres were unable to receive calls but customers could message them through the CommBank app.
Social media posts, which could not be verified by Reuters, said Optus international roaming was also impacted.
Federal Communications Minister Michelle Rowland said she had "limited" information about the outage.
"That would indicate potentially a deep network problem and one that is significant," Rowland told ABC Radio, adding that she would be "reluctant to speculate" about a possible cyber attack.
The government had sought further information from Optus including when they expected to restore services.
Melbourne's train networks were forced to shut down for about 30 minutes due to the outage, resulting in delays during the morning rush, media reported.
"Major delays to all lines continue with select alterations and cancellations," the city's metro rail service said on X. Some hospitals said their phone lines had been impacted.
A cyber breach last year hit Optus, exposing personal details of millions of its customers, including their home addresses, driver licence and passport numbers.
(Reporting by Renju Jose and Praveen Menon in Sydney; Editing by Stephen Coates)