Telstra customers are still having trouble calling triple zero on Thursday morning as the telecommunications giant confirmed a secondary issue stemming from Wednesday's national outage continued to impact calls. This was reported by Qazaqyia.kz citing The Guardian.

Some who tried to call the emergency hotline were receiving an error message and their phones would try to connect to an alternative network, Telstra said. Customers have been urged to wait for the phone to connect to another network, or use a different device to make their call.

The federal communications minister, Anika Wells, told ABC radio: "In some instances calls are going straight to message bank. In some instances, 000 calls were not going through. It has been largely resolved, but there are still residual problems," she said.

In a statement early Thursday, Telstra said: "We're deeply sorry for the impact this issue has had on so many people." As of 6.30am on Thursday morning, Telstra said the occurrence of the secondary triple-zero issue had been reduced by 90%.

But the minister for industry, Tim Ayres, told the ABC on Thursday that "100% is the only acceptable figure here".

The telco's issues have continued to wreak havoc across Australia. All the trains on Victoria's regional rail network were still suspended on Thursday morning, up to and including the morning peak travel period. "The V/Line network continues to be impacted following the nationwide Telstra telecommunications outage, with passenger services unable to operate," V/Line said in a statement on its website.

Wells said she had not yet heard of any "adverse outcomes" linked to the continuing triple-zero issues as Ayres revealed there would be a full investigation into the outages. "Communications and digital infrastructure [are] part of the lifeblood of the economy," he said. "Each of these operators has responsibilities here. The framework is there to manage those, to make sure we've got a transparent investigative framework and to apply penalties where it's necessary."

Thousands of customers were unable to make calls or access data on Wednesday after a software defect affected Telstra's systems, the telco said. The company made more than 300 welfare checks to people who attempted to dial triple zero during the episode. Of those, 238 said they didn't need assistance. The remainder were referred to state and territory police for welfare checks. Six customers said they needed assistance, which was provided immediately.

Telstra's chief executive, Michael Ackland, said on Wednesday the number of calls appeared to be higher than normal. This suggested some may have been dialling triple zero to check if it worked during the outage, which customers have been urged not to do.

The opposition communications spokesperson, Sarah Henderson, defended her decision to call triple zero during the outage. "I accept the criticism, but what I will say is that I am in a unique position holding this government to account," she told 2GB radio on Thursday. "Telstra's network is critical infrastructure, this should simply not be happening."

The telco blamed Wednesday's issues on a software fault that caused the "GPS node" to reset.