SA facing catastrophic fire risk on Friday

Catastrophic bushfire conditions are expected across several South Australian regions on Friday with the state to be hit by a combination of extremely high temperatures, rising winds and dry lightning.

The Country Fire Service said there was a high potential for fires to break out and once they start they would impossible to control.

"Under these conditions, they will be so erratic and move so fast and develop so quickly it doesn't matter how many firefighters, we're not going to stop the forward spread of these fires," Deputy Chief Officer Andrew Stark said.

"These are certainly the most dangerous conditions we've faced this season.

"They're the kind of conditions where we see property losses and unfortunately sometimes lives lost."

The CFS has a full complement of aircraft available and all available crews on high alert.

Areas of SA most at risk include the Mt Lofty Ranges, the southeast and Kangaroo Island.

Forecasts suggested there could be thousands of lightning strikes across SA and with low humidity and lack of rain, they could start many fires.

A cool change was also expected to sweep across SA late on Friday and while that would bring some relief from the intense heat, the associated wind shift could also cause issues for firefighters.

Catastrophic fire risk conditions were declared for six SA districts, the lower Eyre Peninsula, Yorke Peninsula, the Mid North, Kangaroo Island, the lower southeast and the Mount Lofty Ranges.

Temperatures in some parts of the state were expected to get close to 50C with Adelaide forecast to have a top of 46C which would make it the city's hottest ever December day.