By Nick Wilson and Samantha Lock

Disaster has struck twice for Australia’s largest telco, as it grapples with a separate issue preventing some users from making triple zero calls.

It comes as the communications regulator opens an investigation into a network outage on Wednesday that hit transport, businesses, emergency services and healthcare.

While the issue was largely resolved by mid-morning, a separate issue is preventing some users from making triple zero calls while transport networks remain slow or at a standstill.

The company said overnight work had reduced the separate triple zero error by about 90 per cent.

Engineers are continuing work to eliminate the issue, while its welfare checks process remains in place.

The telco said the volume of welfare checks completed on Wednesday was higher than expected, adding the figures were likely inflated by people calling simply to test triple zero.

By Wednesday evening, it had completed 395 welfare checks.

Of those, six people required emergency assistance while 79 were referred to police for physical welfare checks.

Transport operators are continuing to deal with the fallout from Wednesday’s outage.

All regional V/Line train services across Victoria remain suspended while signalling systems are tested following the outage.

Passengers have been asked to avoid non-essential train travel, with some replacement coaches available.

Most regional train services are operating in NSW, though some routes in the Hunter region and southwest of Sydney continue to face delays and cancellations.

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.

On Thursday, Communications Minister Annika Wells said ACMA had begun preliminary investigations into the outage.

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

“I think 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.”

Last year, Ms Wells increased penalties for telcos that fall foul of their triple zero obligations to $30 million.

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.

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