Australian network operator Optus has opened an investigation into a network outage yesterday that impacted Triple Zero emergency calls.

The outage was caused after Optus carried out a network upgrade, however, within this process, a technical failure impacted Triple Zero calls.

Triple Zero (000) is Australia's main emergency service phone number.

During this outage, three people died, according to Optus CEO Stephen Rue, while it's estimated that 600 customers were potentially impacted.

It has not been revealed how long the outage lasted.

"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," said Rue during a press conference, as reported by SBS News.

Optus said that the outage affected a number of calls in South Australia, the Northern Territory, and Western Australia.

“I want to offer a sincere apology to all customers who could not connect to emergency services when they needed them most,” Rue said.

“And I offer my most sincere and heartfelt condolences to the families and friends of the people who passed away. I am so sorry for your loss.  What has happened is completely unacceptable. We have let you down. You have my assurance that we are conducting a thorough investigation, and once concluded we will share the facts of the incident publicly.”

It's not the first time Optus has suffered a significant outage that has impacted Triple Zero services.

Last year, the carrier was slapped with an AU$12 million ($7.93m) fine for an outage in 2023. The outage, which happened on November 8, 2023, lasted more than 14 hours. Triple Zero (000) is Australia's main emergency service phone number.

The fallout from the outage was so severe for Optus, that its CEO at the time, Kelly Bayer, resigned. Its head of networks, Lambo Kanagaratnam, also quit months later.

DCD sends its sympathies to the family and friends of the deceased.