Natural gas supplies have been cut to about 9000 properties in Mount Gambier, in South Australia's southeast.
The APA Group says supplies were disrupted at about 7pm on Wednesday in an area upstream from the city network in part of the supply line operated by Epic Energy.
It is not known when services will be restored.
Customers have been urged not to try to connect appliances to other sources of gas such as bottled LPG which the company says may cause a fire or explosion.
APA Group manages and operates the SA natural gas network on behalf of Australian Gas Networks Ltd.
It says more information on supplies to Mt Gambier will be provided as it becomes available.