Welfare checks spike as second tech glitch hits Telstra

While the issue was largely resolved by mid-morning, a separate "secondary issue" prevented some users from making triple zero calls.

Telstra advised customers to immediately retry emergency calls if they did not go through, with 639 welfare checks conducted to date.

Chief financial officer Michael Ackland fronted media for a second day, describing the company's back-to-back technical mishaps as "an unfortunate incident" that was unacceptable to customers.

"While we addressed the original issue, that subsequent issue remained ongoing and needed to be addressed in a different way," he told reporters.

"Mobile networks are complex, and we will continue to work through further changes to ensure we have the most robust solution but customers can feel confident in calling triple zero."

The company said overnight work had reduced the separate triple zero error by about 90 per cent as engineers continue to eliminate the bug.

Telstra said the volume of welfare checks was higher than expected.

Mr Ackland said the company had completed 639 welfare checks since Wednesday morning.

Of those 402 cases required followed-up voice calls, with 170 calls passed to police.

Seven callers advised they needed assistance, Mr Ackland said.

"Any one missed call is unacceptable," he admitted.

Mr Ackland referred questions about a possible fatality in South Australia because of a failed emergency call to police. 

The accusation was raised by Liberal senator Kerrynne Liddle on social media but police have denied the claim.

"SA Police are not aware nor have any record of any death in South Australia as a result of the Telstra nationwide outage," a spokesperson said.

The Telecommunications Industry Ombudsman Cynthia Gebert said there were still gaps in the emergency communications system that needed to be plugged immediately.

"It's fair to say the Telstra outage yesterday shines a further light on the whole triple zero ecosystem to work much more effectively for end users than it did," she told ABC News on Thursday.

Transport operators continue to deal with the fallout from Wednesday's outage. 

All regional V/Line train services across Victoria were suspended as signalling systems were tested following the outage. 

The outage began about 4.30am on Wednesday after a software issue affected nodes responsible for keeping time across Telstra's mobile network.

The disruption left customers unable to make some calls or access mobile data, while EFTPOS terminals and business services were also affected.

ACMA had begun preliminary investigations into the outage, Communications Minister Anika Wells said on Thursday.

She said she was informed of the network issues about 7am, more than two hours after Telstra first identified issues. 

"I would have liked to have heard earlier," Ms Wells told ABC radio. 

"It would seem there was some sort of delay that will form part of the investigation."

Ms Wells increased penalties for telcos that fall foul of their triple zero obligations to $30 million in 2025.

Asked whether individuals within Telstra should be punished, Ms Wells said her focus was getting services back online.

"And then investigation can take foot, and we can learn out of that, and penalties can be administered, justice can be served," she said.

Experts say Wednesday's outage exposed just how reliant critical infrastructure is on a handful of telecommunications providers.

It is the third major national outage in less than a year for the $56 billion giant, which powers about 25 million Australian mobile services.