A top lawyer says Optus could face 'huge' consequences after three people, including an eight-week-old baby, died after their calls to emergency services were interrupted during a network upgrade.

The major outage affected Triple Zero calls in South Australia, the Northern Territory and Western Australia on Thursday.

'I have been advised that during the process of conducting welfare checks, three of the triple zero calls involved households where a person tragically passed away,' Optus chief executive Stephen Rue said on Friday.

It sparked a scathing response from South Australian Premier Peter Malinauskas.

'I have not witnessed such incompetence from an Australian corporation in respect to communications worse than this,' Malinauskas said.

'I cannot believe that anyone in the senior levels of Optus thought they should craft a media statement and conduct a press conference before advising the South Australian government that they had ascertained two deaths had occurred.

'I think quite frankly that is reprehensible conduct on behalf of Optus.'

Sam Macedone, who has practised as a solicitor since 1970, said Optus could face claims for civil compensation and damages in the fallout of the outage.

Lawyer Sam Macedone (pictured) said Optus could face claims for civil compensation and damages after three people died during an outage that affected three states on Thursday

The major outage affected Triple Zero calls in South Australia , the Northern Territory and Western Australia on Thursday (pictured, an Optus store in Melbourne)

He told Channel Nine's Weekend Today program that Optus had breached its duty of care to its customers during the outage on Thursday.

'You would have to prove that the deaths were as a direct result of the fact that you couldn't get onto triple zero and not for some other reason,' Mr Macedone said.

'If you could establish all those things, then I think Optus is going to face some huge claims for compensation.'

SA Police on Thursday said an eight-week-old boy from Gawler West, 43km north of Adelaide, and a 68-year-old woman from Queenstown, in the north-west, had died.

A third person, who is yet to be identified, died in Western Australia.

Optus' chief executive on Friday confirmed the telco had conducted a network upgrade on Thursday and that a technical failure had impacted emergency calls.

'This resulted in the failure of a number of triple zero calls,' Mr Rue said.

'Our investigation is ongoing, but at this stage I can confirm that approximately 600 customers were potentially impacted, of which a proportion of their calls did not go through.'

Optus CEO Stephen Rue (pictured) said about 600 Triple Zero calls was affected

Optus fined $12million after thousands were unable to call triple-zero during major network outage

Mr Macedone suggested Optus hadn't learned its lesson after it suffered the biggest mobile network outage in Australia's history in November 2023.

Optus was fined more than $12million in penalties for breaching emergency call rules during the outage.

An investigation found the telco had failed to provide access to emergency services for 2,145 people and had subsequently failed to conduct welfare checks on 369 people who had tried to make an emergency call.

Mr Rue said it was 'crucial' that Australians have access to emergency services.

'Before you do any upgrade, you should put in place plans that if something goes wrong you can immediately put things back in operation again, you just can't let the thing fall apart for hours and hours,' the lawyer said.

'There were 600 people that tried to get through and that is just not acceptable and I'm pretty sure that the statutory obligations have been breached all over the place.

'It is non-negotiable and we're talking about deaths here, and if those deaths were caused by the fact that you couldn't get onto triple zero, then huge consequences will follow.'

There are still unanswered questions from the outage, including why only triple zero calls, rather than all calls, were affected.

Communications Minister Anika Wells said the outage was an 'incredibly serious and completely unacceptable' incident.

'The impact of this failure has had tragic consequences and my personal thoughts are with those who have lost a loved one,' Ms Wells said.

'Optus and all telecommunication providers have obligations to ensure they carry emergency services calls.'

Daily Mail has contacted Optus for comment.

The 'huge' consequences for Optus after three people died in outage