The Greens have called for a federal parliamentary inquiry to examine what led to a nationwide outage of the Optus network.

Millions of customers were left without phone and internet services after the network dropped out from about 4am on Wednesday.

Greens senator Sarah Hanson-Young said the party would move to set up an inquiry into how the network was brought to a halt.

“We need to make sure that all Australians have access to affordable and reliable internet and telecommunication, because otherwise, life as we know it stops, and that’s what Australians right around the country experienced this morning,” she told reporters in Canberra.

“This is not a small matter, and the parliament will have to look at what Optus can and should be doing, what they knew, how this failure happened, and there needs to be consequences of this type of outage.”

The Greens will push to set up the inquiry in the Senate later on Wednesday. It was not known if the government or opposition would back the parliamentary probe.

Senator Hanson-Young accused Optus chief executive Kelly Bayer Rosmarin of a lack of accountability in her response, after she only did one media interview in the hours after the network went down.

“Australians are rightly angry today that their phones are not working, their internet is dead, and the CEO of Optus has phoned it in. Not good enough,” she said.

“This is not the first time that Optus have not been upfront with customers in a timely manner.”

The Greens also urged the government to do everything it could to assist the telco during the outage, including finding alternatives to access emergency services.

Ms Bayer Rosmarin confirmed people could not make calls to triple-zero on Optus landline devices although it was still possible to do so on a mobile phone.

Communications Minister Michelle Rowland said Optus needed to be transparent with customers.

She said the millions of Optus customers affected 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 in Sydney.

“It is important at this time that people have their services restored as soon as possible.”

Agriculture Minister Murray Watt told parliament the outage of the network was distressing for customers.

“The government has made clear to Optus that restoration of its network is a priority and we will continue engaging with Optus as a matter of urgency,” he said.

“It goes without saying that connectivity is essential for Australians, which is why the impact of this outage on consumers, businesses and services including hospitals and public transport networks is very concerning.”

Optus yet to reveal cause of major national outage

WHAT HAPPENED DURING THE OPTUS OUTAGE

* Optus first noticed issues with services at 4am on Wednesday and said engineers were investigating a network fault

* The outage impacted customers using its phone network and internet services

* The telco said landline calls to triple zero were not working, however mobile calls were still going through

* Services started to resume just before 1pm

* There is no indication of a cyber attack, according to Optus chief executive Kelly Bayer Rosmarin

* The cause of the issue has not been revealed

WHAT WAS SAID

* Communications Minister Michelle Rowland called on Optus to “step up” its communication with customers 

* The Telecommunications Industry Ombudsman advised affected customers to lodge a complaint if they contacted Optus and were unhappy with the response

* Greens Senator Sarah Hanson-Young called for a senate inquiry into the outage

* Deputy opposition leader Sussan Ley said telcos needed to have better plans to communicate with customers during outages

* SA Premier Peter Malinauskas said the state would reconsider contracts with Optus because reliability was important

WHO WAS IMPACTED

* Millions of personal and business customers

* Services on Melbourne’s rail line Metro Trains stopped for just over an hour with the issue attributed to a communications outage

* Health services impacted to varying degrees included private hospital operator Ramsay Health, NSW Health call centres, the NSW Poisons Hotline, The Royal Melbourne Hospital, Northern Health in Victoria, Ambulance Victoria and SA Health

* Some ACT government phone lines were also impacted.