All Telstra mobile customers will enjoy free data on Sunday after a major nationwide outage affected its mobile network today.

Telstra this afternoon revealed the outage, which affected data and voice calls, was the result of a mistake by one individual.

"This is an embarrassing human error. It's not OK. We do not like causing that level of inconvenience to our customers," Telstra chief operations officer Kate McKenzie said.

She said there would be a full investigation.

Telstra has since announced all mobile customers will receive free data all day Sunday as compensation.

The issue started when one of the nodes used to manage voice and data traffic between devices and the network started to malfunction.

"We took that node down, unfortunately the individual that was managing that issue did not follow the correct procedure, and he reconnected the customers to the malfunctioning node, rather than transferring them to the nine other redundant nodes that he should have transferred people to," Ms McKenzie said.

"Unfortunately this had a flow on consequence and it lead to massive congestion across the rest of the nodes.

"I can now happily say we restored services to all of our customers. Our first and most important priority was making sure voice traffic, data traffic across all of our customer base was restored as quickly as possible. I can say that has now happened.

"We are working very quickly right now to figure out how we can provide some free data to our customers to make up for the inconvenience that has been caused today."

Customers across the country took to social media earlier today to report issues with data and voice calls, as well as some issues with landline calls.

“We are aware of an issue currently affecting mobile voice and data nationally. We are working to resolve the issue as quickly as possible and thank customers for their patience,” Telstra earlier said in a statement.

One Telstra user, who identified himself as Angus, said he had called Telstra about the issue and had been told to come to his local branch.

"I take an hour out of my day, get down here, and they say it's an outage," he told 9NEWS, before adding, "it hasn't been a bad day. Things happen in life and no one died."

"It's just really hopeless, things go wrong, but they could have done something better."

Police have clarified that even during an outage, it is still possible to call triple zero if you are in range of another network.

Outages appear to be affecting Victoria, South Australia, Western Australian, Queensland and New South Wales.

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