Telstra announced the fire location to be Chatswood Exchange, Sydney, via Twitter.
Users on website http://www.aussieoutages.com are complaining of outages of landline, mobile and NBN services from Australia's biggest telecommunications company.
The outage map on the shows all states and territories are affected, including Melbourne and Sydney.
Screenshot from outage website aussieoutages.com showing affected areas.
The incident follows a fire last year at another exchange in Brunswick, Melbourne, caused by faulty wiring.
The outage has affected businesses also, including Jetstar.