Telstra mobile network crashes nationwide, causing transport and payment delays

Telstra says its services have been mostly restored after its mobile network suffered a major nationwide outage, affecting potentially millions of customers.

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 continuing to restore remaining services impacted by the outage.

Telstra says its services have been mostly restored after its network suffered a major, nationwide outage that left potentially millions of Australians unable to make phone calls or access the internet.

"We've made good progress restoring services, with just under 90 per cent of calls and data now flowing successfully across the network," a spokesperson said in a statement.

"Our teams are working as quickly as possible to restore remaining services and get all customers back online."

Follow the latest developments in the Telstra network outage in our live blog.

Telstra's chief financial officer Michael Ackland told reporters there was no evidence to suggest "malicious activity" might have sparked the outage, but said the telco did not know what the "root cause" was.

Mr Ackland said he believed the outage might have stemmed from issues within data centres operated by Telstra in Sydney and Melbourne.

"Telstra is investigating, but we will work closely with them."

Earlier on Wednesday, the outage affected 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.

Telstra's mobile network has suffered a major, nationwide outage. (ABC News: Lucas Hill)

Hundreds of traffic lights in South Australia were also impacted, operating on basic programming rather than responding to traffic conditions.

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 being rerouted to use other providers' mobile networks, and emergency services in Vi