Regional trains have been cancelled for a second day after Telstra’s outage halted the service indefinitely, leaving commuters in the lurch.

Commuters vented their frustration as they waited for replacement coaches at Melbourne’s Southern Cross Station on Thursday morning.

The outage began at 4.30am on Wednesday, but despite Telstra restoring phone calls by Wednesday night, Victoria’s regional railway is still offline and it’s unknown when it will be back up and running.

V/Line chief executive Will Tieppo said work had been done overnight to repair connectivity between train radio systems and the control centre.

“We are now in the process of undertaking testing for each of the train units that we’ve got here in Melbourne,” Tieppo told reporters at Southern Cross Station on Thursday.

He said he hoped to have services back up by Thursday’s afternoon peak, but made no promises after his earlier ambitions for a Wednesday afternoon return fell through.

Some commuters were forced to spend the night in city hotels because V/Line did not have enough buses to replace more than 300 cancelled services.

On Thursday, platforms at the train station were largely free from traffic, while commuters filtered into the bus terminal for a limited number of replacement services.

V/Line staff were out in force, distributing snacks to families, couples and returning holiday-makers as service announcements played overhead.

Elderly woman Pam Promnicz was having a hard time getting back to Warrnambool, concerned she had too many bags for the coach.

“I’d much prefer to be on the train,” she told AAP.

She claimed her V/Line service leaving Warrnambool before the Telstra outage had also been disrupted, though for different reasons.

“That’s Victoria for you,” she said.

Brian Rigby, who happens to be a network engineer, said the disruptions could have been avoided if the V/Line was not so dependent on the Telstra network.

“When Telstra has an outage, they’re big ones,” he said.

“It makes you wonder what happens if next time they go down and stay down.”

He said Thursday’s cancellations added two train legs to his trip from the Pilbara to Traralgon.

“I’ve already been travelling for 15 hours, so this just makes it that little bit longer,” he said. “We’re used to it, really.”

Australia’s largest telco is blaming a software defect for the crippling outage, which caused nationwide disruptions, potentially affecting millions of phone-users, travellers and shoppers.

Telstra’s Michael Ackland has blamed the outage on a software defect.

Telstra chief financial officer Michael Ackland said the telco was continuing to investigate but it was confident its teams had identified and isolated the defect.

The $56 billion giant that powers about 25 million Australian mobile services said its network issues had been fully resolved by 4pm on Wednesday after the outage, which began in the early morning.

Pervasive network problems left users unable to make calls or access data on their mobile phones, while some EFTPOS transactions were also affected.

On Thursday, Communications Minister Annika Wells said the telecommunications regulator ACMA had begun preliminary investigations into the outage, which affected transport, businesses, emergency services and healthcare.

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

Meanwhile, Opposition communication’s spokeswoman Sarah Henderson has doubled down over her decision to make two calls to the triple-zero network after the outage.

Making false calls to triple zero is a criminal offence with a maximum penalty of three years in prison, and Henderson’s test calls have been criticised by Labor as irresponsible.

But the senator has insisted she was within her right to make the test calls.

“I was simply, as the shadow minister for communications, making those initial calls to work out whether the … system was actually operating,” she told Sydney radio station 2GB on Thursday.

“I accept the criticism, but what I will say is that I am in a unique position holding this government to account.”

–AAP