The warning has been declared for South Australian regions close to Port Augusta and Port Pirie for tomorrow.

Catastrophic is the highest possible warning, and was created after Black Saturday.

Warnings have also been issued for Victoria for tomorrow, with Department of Sustainability fire chief Ewan Waller saying the period between today and Friday loomed as an "extended period" of danger.

A combination of heat and thunderstorms will begin to roll across Victoria today, with "extreme" conditions to be declared for some regions tomorrow.

Meanwhile, Victorian Premier John Brumby said he hoped to be given a trial of Telstra's new national emergency warning communication system in coming weeks, and that it should be operating by January or February.