The federal government will hold an industry-wide inquiry following an Optus outage that left millions of Australians unable to make calls or connect to the internet.

Announcing the review on Thursday, a day after the day-long outage, communications minister Michelle Rowland said the impact of the loss of connection was particularly concerning.

The outage was first reported at 4am on Wednesday and it wasn’t until 6.30pm that evening that Optus said ‘most services’ should have been restored.

Ms Rowland told the ABC it appeared to have have been caused by a ‘serious fault’ in Optus’s core network which affected mobile, broadband and landline services.

She added the government hadn’t yet received a definitive explanation from Optus.

*Update: On November 13 Optus issued a statement saying changes to routing information from an international peering network following a routine software upgrade caused the outage.

“It is critical the government conducts a process to identify lessons to be learned from yesterday’s outage,” Ms Rowland said.

“I will task my Department with developing the terms of reference for a post incident review.”

The minister also indicated that some government departments that currently use Optus may consider dumping it.

“I know that there are certain government departments and agencies at all levels who were utilising Optus,” she told Sky News.

“I note some of them have made comments that they are looking at alternative suppliers. It is a competitive market … I think that individual departments and organisations and consumers will be making their own assessments on that.”

Review will consider impact on emergency calls

Ms Rowland said the review will aim to shed light on what went wrong and its impact on the Triple Zero service. It will also help providers improve their response after an outage, she said.

“I think the terms of reference here also need to apply across the industry because we need to take those lessons for the other carriers and service providers as well,” she said.

The government would provide further announcements about the terms of reference, and next steps in the review in due course, the minister said.

ACMA investigation

The national communications regulator ACMA said it had launched a separate investigation in relation to emergency calls.

“The ACMA has commenced an initial assessment to investigate Optus’ compliance with rules requiring telecommunications carriers to ensure that emergency calls are successfully carried from each telecommunications provider to the Emergency Call Person (Telstra),” it said in a statement.

Later on Thursday, the Greens announced that the outage will also be the subject of a Senate inquiry.

“This Inquiry will be vested with the powers of the Senate to compel Optus bosses to appear publicly and provide the answers and the solutions that Australians deserve,” inquiry chair Senator Sarah Hanson-Young said.

“The inquiry will also look into the role of the Commonwealth Government in ensuring Australians have access to essential, reliable telecommunications going forward.”

Optus Vice President of Regulatory and Public Affairs Andrew Sheridan said the carrier looked forward to fully cooperating with the proposed reviews by both the Department of Communications and ACMA.

“As a critical infrastructure provider, we understand how important it is to ensure continuity of service and any lessons learnt are likely to be helpful for both Optus and others in our industry,” he said in a statement.

“Optus once again apologises to our customers and others that were impacted by the outage.”