Telstra mobile customers have been hit with a second outage in less than a month.

For the second time in less than a month, many Telstra customers have been unable to make calls or access data.

Prepaid mobile customers were left without phone or data services early on Wednesday morning before Telstra managed to restore data by 0900 AEDT and calls an hour later.

"Some of our pre-paid mobile voice and broadband customers may have experienced issues making calls, recharging their credit and accessing the internet this morning," a Telstra spokesman said.

It is unclear how many prepaid customers were affected by the outage and some may still have problems making overseas calls he said.

An earlier outage in February left 1.5 million Telstra customers without service, prompting Australia's biggest telco to offer a free day of data for users.