Risk reduced from SA bushfires

The Country Fire Service has downgraded warnings for two major fires burning in South Australia.

South Australia remains on high bushfire alert as temperatures continue to soar across the state. (AAP)

The threat to lives and property from two serious bushfires burning in South Australia has eased.

The Country Fire Service has downgraded warnings for the fires near Birdwood in the Adelaide Hills and near Stansbury on Yorke Peninsula to watch and act messages.

However, the CFS says both are not yet contained.

It says the forward spread has been halted but there is still active fire around the perimeter.

There have been no immediate reports of any major damage to houses or other buildings.

Both fires were sparked in stubble and were being driven by strong winds and high temperatures.

"Conditions are almost as bad as they can be," Country Fire Service assistant chief officer Rob Sandford said at the height of the emergency.

A third watch and act message was issued on Monday for a fire near Coonalpyn, in the state's southeast, which was also burning uncontrolled in stubble.

The CFS said that fire had destroyed one shed and crews were actively trying to defend another.

The fires came as temperatures in Adelaide topped 36C on Monday.

The Bureau of Meteorology said winds would ease into the evening.