Optus Mobile network is down for the entirety of Australia

Optus mobile services are down across the country, affecting millions of Australian customers and businesses.

The outage was first reported at around 4am AEDT, with Optus customers across the country taking to social media to find out what was happening.

Mobile phones are unable to make and receive calls and mobile internet services are also down.

A message on the Optus website says that its engineers are currently investigating a network fault that is impacting customers.

It has also responded to customers on the social media site X, formerly known as Twitter, saying that its working to restore services as a priority.

The ABC has contacted Optus for comment.

Train services were briefly interrupted in Melbourne due to the outage.

Metro Trains said its back-up system, which uses the mobile network, was affected by the outage.

Services have now resumed but passengers are being warned there will be delays.