Extreme bushfire conditions have been declared across much of South Australia as the state continues to swelter through its worst heatwave in more than three years.

The Country Fire Service says the bushfire risk is extreme from the west coast to the upper southeast, including the Adelaide Hills with total fire bans in place.

The Bureau of Meteorology has forecast a top temperature in Adelaide on Thursday of 41C, on day three of the five-day scorcher.

The mercury is also tipped to hit 41C on Friday before a cool change sweeps through early on Saturday, dropping temperatures to the mid-20s.

That will make it the longest string of days of 35C or more since December 2019.

The conditions have prompted authorities to activate heatwave emergency plans, with the State Emergency Service urging people in the hottest regions to stay indoors if possible.

In some regional centres, temperatures will surge into the mid-40s, including Nullarbor which is forecast to reach a top of 45C on Thursday.

Community centres in Adelaide have been opened for rough sleepers and homelessness services are conducting outreach programs around the city.

The Red Cross will also provide free healthcare checks by phone.


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