COUNTRY Fire Service crews are battling a bushfire in South Australia's mid-north.

The CFS said the blaze was about 4km west of Hoyleton.

They have urged people in the area to activate their bushfire survival plans.

The blaze comes as much of South Australia swelters through another day in the low to mid 40s.

Just before 2pm (CDT) the mercury hit 40.6C in Adelaide while at Wudinna, on Eyre Peninsula,it hit 46.5C and at Port Augusta it reached 45.3C.

But the Bureau of Meteorology said conditions would be milder tomorrow and Wednesday, forecasting top temperatures in the city of 33C and 27C.