The network dropped out about 4am on Wednesday, with Optus customers and businesses unable to connect to the internet or make or receive calls.
An Optus spokesman confirmed some of its services were gradually being restored from about 1pm.
“This may take a few hours for all services to recover and different services may restore at different sites over that time,” the company statement said.
“We reiterate our apology to customers for the nationwide service outage that has occurred this morning.”
Close to 10 million Optus customers had their personal information stolen when the company’s data system was breached last year.
There was no indication Wednesday’s outage was the result of a cyber attack, chief executive Kelly Bayer Rosmarin said.
We’re aware of an issue impacting Optus mobile and nbn services and are working to restore services as quickly as possible. We understand connectivity is important and apologise for any inconvenience caused.— Optus Help (@optus_help) November 7, 2023
“We do everything we can to give great service to our customers,” she told ABC Radio Sydney, calling into the station via WhatsApp.
“We’re really sorry that this outage has occurred and we’re working to restore services for our customers as a priority.”
Ms Bayer Rosmarin confirmed people could not make calls to triple zero on Optus landline devices during the outage, although it was still possible to do so on a mobile phone.
Federal Communications Minister Michelle Rowland said Optus needed to be transparent with its customers, who were experiencing “a high level of anxiety and frustration”.
“Consumers will be making judgments about the quality of service that they receive in a competitive market,” she told reporters.
“It is important at this time that people have their services restored as soon as possible.”
Ms Rowland encouraged consumers, especially small businesses, to keep receipts in case they choose to pursue any compensation.
The Telecommunications Industry Ombudsman also advised affected customers to lodge a complaint if they had contacted Optus and were unhappy with the response.
Michelle Rowland advised Optus customers to keep receipts if they want to pursue compensation.
Greens Senator Sarah Hanson-Young called for a Senate inquiry into the outage, saying it was important for Australians to have confidence in essential phone and internet services.
“This is not a small matter and the parliament will have to look at what Optus can and should be doing … and there needs to be consequences,” she told reporters.
South Australian Premier Peter Malinauskas said his government would reconsider its contracts with Optus because reliability was important.
“They will have to explain for themselves and I think they should be held to account,” he told reporters.
National Retail Association director Rob Godwin said the outage was a blow to retailers and small businesses seemed to be the most adversely affected.
“EFTPOS is down for non-Optus users as well, and it can’t be fixed today since some of the big banks are uncontactable,” Mr Godwin said.
“This is costing businesses thousands of dollars in sales.”
All Melbourne metropolitan train services were stopped from about 4.30am on Wednesday because of a communications fault across the train network, reportedly due to the outage.
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 told AAP in a statement.
Service NSW call centres, Victoria’s virtual emergency department and Northern Health hospital phone lines were also down during the Optus outage.