By Renju Jose

SYDNEY Australian No. 2 telco Optus on Wednesday reported an outage across its mobile phone and internet networks affecting millions of customers but the company did not specify if it was due to a cyber incident.

A cyber breach last year hit Optus, the Australian unit of telecoms firm Singapore Telecommunications, exposing personal details of customers, including their home addresses, driver licence and passport numbers.

Optus has just over 10 million customers, about 40% of Australia's population.

"We're aware of an issue impacting Optus mobile and (broadband) services and are working to restore services as quickly as possible," the company said on messaging platform X.

Social media posts, which could not be verified by Reuters, said international roaming was also impacted.

Federal Communications Minister Michelle Rowland said she had "limited" information about the outage, which has impacted networks for several hours.

"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.

(Reporting by Renju Jose in Sydney; Editing by Chris Reese and Stephen Coates)