Optus says its landlines cannot be used to make emergency calls as a nationwide outage stretches on with no fix yet in sight.

The telecoms company confirmed on Wednesday morning that the outage meant its landlines could not be used for triple-zero calls.

They can still be made from Optus mobiles.

It came as Optus chief executive Kelly Bayer Rosmarin called into a Sydney radio state via WhatsApp to give her first update on the outage that is thought to have affected up to 10 million customers across Australia.

She apologised for the outage, and denied it was due to a cyber hack or software issue.

“It is highly unlikely [to be software-related]. Our systems are actually very stable, we provide great coverage to our customers, this is a very rare occurrence,” Bayer Rosmarin told ABC radio.

“When I have more information about the root cause, I will be the first to let our customers know.”

Bayer Rosmarin said the company first learned about the issues shortly after 4am on Wednesday (AEDT). She gave no timeframe for the problems to be resolved.

On its website earlier, Optus said its engineers were investigating a network fault. Mobile phone users are unable to make or receive calls and mobile internet services are down.

Asked how people should stay updated if they had no internet access, Bayer Rosmarin said Wi-Fi connections were widely available.

“There are definitely places where people can connect to Wi-Fi; there are plenty of organisations that offer Wi-Fi. Our stores have connectivity, [and] our messaging is still working through the my Optus app,” she said.

“We hope that customers are taking advantage of all of the other avenues during this period where our service is being returned.

“We will do everything we can to get services back. The teams are trying many different angles and we will not rest until the service is back up for our customers.”

Tweet from @optus_help

Federal Communications Minister Michelle Rowlands said it was vital that Optus was “transparent and timely” in its customer updates.

“It is essential that we have that timeliness and the transparency to give consumers confidence about what is a vital part of our infrastructure and services in this country,” she said.

Rowland said the issue was a “deep fault”.

“It has occurred deep within the network. It has wide ramifications across mobile, fixed, and broadband services for Optus customers,” she said.

Rowland said it was a government priority to keep Australians safe, including with access to emergency calls.

“The government stands ready to do everything we can to assist Optus at this time but, in particular, to assist consumers in understanding what the current situation is,” she said.

South Australian Police issued a statement on Wednesday, urging Optus customers to call triple-zero only in an emergency.

“If Optus customers cannot contact the police assistance line on 131 444, they are asked to attend a police station to report a crime. It is not known when the outage will be resolved,” it said.

Optus problems have been reported across Australia. Image: DownDetector

Rowland said Optus should “step up” to keep its “clearly frustrated” customers up to date.

“We are now at 11 o’clock. For a lot of people who are trying to get on with their day in their businesses, this is absolutely vital that they get back to normality,” she said.

“I would urge Optus to utilise every channel available, including the broadcast media, to ensure these messages get across. We rely so much on our communications devices, including for consuming media. And when that isn’t available, that is noticeable.

“I think it is important for Optus to continue to step up. Customers expect this. Customers are clearly frustrated about it and Optus should respond to that accordingly.”

There are also significant issues for many businesses, including with EFTPOS transactions.

The Commonwealth Bank has warned customers there might be some issues with online banking services as a result of the outage.

“You may encounter difficulties calling us and receiving SMS from us including Netcode,” CBA said in a pop-up alert to users of its app.

Tweet from @johnj1138

Earlier on Wednesday, train services across Melbourne were interrupted, reportedly due to the Optus outage.

All metropolitan services were stopped from about 4.30am due to a communications fault across the train network.

Metro Train services started to resume just before 6am but major delays continued throughout the morning peak as services were restored.

“We apologise to our passengers for the delay to their travel this morning,” Metro Trains chief executive Raymond O’Flaherty said.

“We thank passengers for their patience while trains return to their normal timetable.”

Service NSW call centres were also down, as were phone lines across Northern Health’s hospitals and virtual emergency department in Melbourne’s north.

Barwon Health in southern Victoria said it had also been affected.

-with AAP