SA swelters through a scorcher

South Australia has sweltered through a summer scorcher with temperatures in the west and northern parts of the state soaring into the mid-40s.

Ceduna, on the state's west coast, was among the hottest spots with the mercury reaching 47.1C on Thursday.

Other centres were almost as hot including Oodnadatta with 46.3C, Nullarbor with 46.2C and Port Augusta with 45.5C.

In Adelaide the top at the Kent Town observation centre hit 42.3C.

But the Bureau of Meteorology said a cool change was slowly edging across SA and dropped the temperature by 10 degrees at Nullarbor in just eight minutes.

The cooler conditions are expected to reach Adelaide during Friday morning with the city forecast to have a milder top of just 31C ahead of even cooler conditions across the weekend.

The Country Fire Service reported no major incidents with the worst being a fire in a hay truck at Auburn in the mid-north.