Telstra is experiencing an outage in voice calls, mobile data, and home internet services.
The outage is classed on Telstra's service status page as a "current interruption", and is affecting 2G, 3G, 4G, National Broadband Network (NBN), ADSL, and PSTN services across the country.
The telco also noted that "some customers may experience difficulties accessing or using prepaid services".
A Telstra spokesperson said the company is currently investigating the causes of the outage, as well as when it will be resolved.
"We are aware of an issue currently affecting mobile voice and data nationally," the spokesperson said.
"We are working to resolve the issue as quickly as possible, and thank customers for their patience."
The outage comes a day after fixed-line telecommunications provider TPG advised its customers of a major submarine cable outage between Sydney and Guam, which is not expected to be repaired until 8am on March 7.
Telstra also had its own Australia-Singapore subsea cable outage in October last year, which caused severe delays for customers attempting to download or update their operating systems or apps across the iTunes Store and the App Store, as well as use streaming services Apple Music and Apple Radio.
Updated at 1.22pm AEDT, February 9: Added comment from Telstra spokesperson.