The Australian government said Saturday that telco firm Optus "let Australians down" after three people died during a network outage that prevented calls to emergency services.

The outage impacted 600 people across South Australia, Western Australia and the Northern Territory on Thursday evening for at least ten hours.

Authorities said they were not informed of the incident or deaths until late Friday.

Communications Minister Anika Wells said Saturday the telco company had "let Australians down when they needed them the most and this isn't good enough."

"Optus and all telecommunications providers have obligations under Australian law to ensure that they enable emergency services' calls."

Wells added it was "not good enough" that Optus did not appear to know enough about why the failure occurred and why alarms did not go off 24 hours after the outage.

Wells said an investigation by the communications watchdog was underway.

South Australian Police said the deaths of an eight-week-old boy and a 68-year-old woman were linked to the outage.

The third death occurred in Western Australia, local media reported.

South Australian Premier Peter Malinauskas slammed Optus for its "reprehensible conduct."

"I have not witnessed such incompetence from an Australian corporation in respect to communications worse than this," he told reporters Friday.

Optus chief executive Stephen Rue said the incident was "completely unacceptable" and that the company was investigating the matter.

"I want to offer a sincere apology to all customers who could not connect to emergency services when they needed them most," he said in a statement late Friday. "And I offer my most sincere and heartfelt condolences to the families and friends of the people who passed away."

The telco could face fines and other legal penalties.

Optus was previously fined Aus$12 million after an outage halted its mobile and internet systems for nearly 12 hours in 2023.