The telco, which powers about 25 million mobile services across the country, confirmed on Wednesday it was investigating the issue with thousands unable to make calls and access data on their phones.
Telstra chief financial officer Michael Ackland expressed regret for the outage, describing it as intermittent but widespread.
"At this stage, we do not know what the root cause was. I'd rather let the investigations play out," he told reporters in Melbourne.
He assured the public triple-zero calls follow different settings and were not impacted in the same way as other mobile calls, but the company had conducted a number of welfare checks.
"We can monitor all calls that are attempted and failing and we have been conducting welfare checks on those," Mr Ackland said.
"We are continuing to investigate every angle on where it may have impacted triple zero, if that has occurred."
The outage affected triple-zero calls in WA, according to the state's police force.
"If you are affected and do not have access to an alternative mobile or landline service, police recommend making arrangements with a neighbour, family member, or friend so you can access a working telephone in an emergency," WA Police said in a statement.
The telco giant said it had made "good progress" restoring services with about 90 per cent of calls and data flowing successfully.
"We know how much our customers rely on our network and understand just how much of a disruption this is to your day," the company said in a statement.
"For that we're so sorry. We'll share further updates until all is resolved."
Minister for Emergency Management Kristy McBain said the government was told the network disturbance had a wide-ranging impact, including on public transport.
She confirmed the service disruption brought all Victoria's regional train services to a halt, leaving thousands of passengers stranded in the morning midweek rush.
The V/Line network said no trains are able to run on the tracks with a very limited coach replacement in place, as commuters are asked to avoid travel until further notice.
Across the border, Transport for NSW said trains on its Hunter Line.
Trains were also not running between Campbelltown in southwest Sydney and Moss Vale and Goulburn.
Eftpos machine company Tyro also reported its transactions have been hampered without specifically naming the provider.
Mr Ackland insisted customers should still trust the largest network provider.
"Australia can absolutely have faith in its biggest telco, and that is Telstra," he noted.
"We take these outages very, very seriously. Our investment in resilience and cybersecurity and redundancy in our network is significant, but it is a big and complex network."
Telstra asked users to restart their devices as a temporary fix.
More than 7500 customers reported the network disturbance on online monitoring platform Downdetector.
The latest outage comes after other telecommunications giants Vodafone and Optus experienced recent gaffes that proved fatal.
In June, Vodafone customers were left with intermittent reception and data issues across Australia.
The telco said customers who could not access the network were able to use triple zero by connecting to other available mobile networks.
Two deaths have been linked to an outage at Optus in September 2025, which lasted almost 14 hours and affected hundreds of calls in four states and territories.
