Breaking: Telstra users report mobile network has crashed across Australia

Telstra's mobile network appears to be suffering a major outage across the country. (ABC News: Lucas Hill)

Telstra's mobile network has suffered a major nationwide outage, affecting millions of customers and causing delays to public transport networks.

Some regional train services in NSW and Victoria have been suspended, and taxi passengers are reporting they are unable to complete payments.

Telstra says it is looking into the issue and will share an update once it is fixed.

Telstra's mobile network has suffered a major, nationwide outage, leaving millions of Australians unable to make phone calls or access the internet.

The outage is also affecting payment systems and public transport across the country, with regional rail lines in NSW and Victoria and the ACT's MyWay+ ticketing system among those services affected.

The outage appears to have started early on Wednesday morning, with outage monitoring site Downdetector.com showing a large spike in reports beginning about 5am AEST.

Downdetector.com shows a huge spike in Telstra outage reports shortly before 6am. (Supplied: Downdetector.com)

Users of other mobile providers that operate on Telstra's network, including Boost, Aldi, Tangerine, Belong and Everyday Mobile, are also reporting outages.

However, the outage does not appear to be affecting all the telco's customers, with some reporting on social media that they are still able to make calls, access the internet, or both.

Calls to Triple Zero (000) should be unaffected by the outage, with calls rerouted to use other providers' mobile networks.

Carol Bennett believes self-regulation within the telco sector is not working, and says there's a risk of more connection failures unless the government and its telecommunications regulator act now.

A Telstra spokesperson told the ABC the company is looking into "an issue affecting some mobile calls and data connections".

"If you're having trouble connecting, try again as it may work on a retry," the spokesperson said.

Trains between Newcastle Interchange and Maitland on the Hunter Line have stopped running due to the outage, with replacement buses on the way.

The Southern Highlands line between Campbelltown and Moss Vale/Goulburn is also affected.

In Victoria, all regional train services have been suspended by service operator V/Line, including the Bendigo, Seymour, Gippsland, Geelong and Ballarat lines.

Josh Meadows was set to commute from Castlemaine to Melbourne this morning when, after his train arrived at the station, he heard an announcement that it couldn't proceed due to a "Telstra radi