Some properties are thought lost or damaged and others remain under threat from two serious bushfires burning near Adelaide.

The Country Fire Service says 28 fires have been sparked across the state amid catastrophic fire conditions on Friday.

Two have sparked emergency warnings, in the Adelaide Hills and at Angle Vale, in the northern suburbs, and CFS chief Mark Jones said they were unlikely to be contained soon. A third emergency warning was issued on Friday afternoon for the blaze at Maitland in the York Peninsula.

Mr Jones said the terrain and the prevailing conditions in the Adelaide Hills, were proving particularly challenging for fire crews.