Australian officials have promised telecommunications giant Optus will face significant consequences over a systems outage linked to multiple deaths.

The incident last week left hundreds of people across more than half of the country unable to call emergency services for 13 hours.

Optus - one of the country's two major providers - says at least three people died as a result, and its chief executive has apologized to their families and the public for the completely unacceptable failure.

The company is under fire for its delayed handling of the incident - the second such outage for the firm in two years - and the nation's communications regulator is investigating.

More than 600 calls to emergency services failed last Thursday, primarily coming from South Australia, Western Australia and the Northern Territory. At least two calls to triple-0 made from south-western New South Wales also did not connect.

However, Optus waited 40 hours to inform the public about the incident and also did not tell regulators until the issue was resolved - counter to standard practice, according to the Australian Communications and Media Authority (Acma).

In a press conference, Optus boss Stephen Rue blamed the outage on a technical fault identified during a network upgrade.

Rue confirmed three people had died, including a baby boy, though police noted that the network failure was unlikely to be a cause in that case. Other authorities in Western Australia also mentioned a fourth person who may have died after their call to triple-0 failed.

Rue stated that multiple customers tried to notify the company of the network issue, but the complaints weren't escalated or handled adequately.

I would like to reiterate how sorry I am about the very sad loss of the lives of four people who could not reach emergency services in their time of need, he said on Sunday.

Acma reacted to the situation, expressing deep concern over the handling of the affair. Australians must be able to contact emergency services whenever they need help. This is the most fundamental responsibility every telco provider has to the public, said an Acma spokesperson.

Communications Minister Anika Wells remarked that telecommunications providers had no excuse for triple-0 call failures and communicated her disappointment regarding the frequency of such incidents. Calls for Optus's chief executive to consider resigning have emerged as the company receives backlash for what has been described as an enormous failure on the Australian people. Investigations continue as Rue intends to provide daily updates.