The telecommunications company is now facing significant criticism and calls for an inquiry after its network dropped out around 4am on Wednesday, with Optus customers and businesses unable to connect to the internet or make or receive calls.

The telco 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,” a company statement said.

“We reiterate our apology to customers for the nationwide service outage that has occurred this morning.”

The State Government also said this afternoon that switchboards at the Royal Adelaide, Lyell McEwin and Flinders hospitals have been restored after going offline during the outage.

Phone services are also operating again for South Australia’s mental health triage service, which the government earlier today said was its “top line” concern.

The outage this morning caused “substantial inconvenience” for SA Health, Malinauskas said, but there were no “clinical implications on the ability of SA Health to look after its patients”.

“Our emergency services and our emergency response – they are all operating as we would reasonably expect them to,” he said at a midday press conference with the SA Health CEO, Health Minister and acting Police Commissioner.

The outage impacted other agencies including Service SA, SA Water, Adelaide Metro and the government’s emergency alert app, Alert SA.

Malinauskas criticised Optus for both the outage and its subsequent communication.

“We are disappointed with Optus, they’ve let their customers down across the state, including the government,” he said.

“Optus need to respond swiftly, communicate effectively with everybody about exactly what is going on here.

“There hasn’t been a great degree of communication coming out about this up until this point, which I think is disappointing.

“Telecommunications now is central to the functioning of the Australian economy, and it has a big impact on services across governments.

“And if Optus wants to see government as a customer then they need to be able to be a reliable service.”

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 said.

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 do everything we can to give great service to our customers,” she told ABC Radio Sydney.

“We’re really sorry that this outage has occurred and we’re working to restore services for our customers as a priority.”

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.”

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.

“We can help you with refunds for the time you have been unable to use your service, compensation claims and disputes about your contract,” the statement read.

-InDaily staff writers and AAP