SOUTH Australians are bracing for a scorcher with fire authorities on full alert as temperatures across the state soar into the 40s.

Fire bans have been declared in all districts including the Adelaide metropolitan area with the fire risk in seven of those considered extreme.

Adelaide was forecast to have a top temperature of 40C, giving the city its seventh day in a row above 30, an unusually long hot streak for November.

A cool change was expected to sweep through the city tomorrow, dropping the maximum back to 31C before falling back into the mid-20s over the weekend.

Yesterday, the Country Fire Service was called into action on several occasions, with the most significant incident a scrub and grass fire at Kringin, in South Australia's east.

Fire crews were also still monitoring the Coomunga fire on Eyre Peninsula which destroyed 2200ha of scrub last week and came within 5km kilometres of Port Lincoln.

Crews patrolled the fire perimeter on foot using thermal imaging equipment to monitor hot spots that had the potential to flare up.

Incident Controller Tony Costello said crews were preparing for high temperatures and north-westerly winds.

"While we have reduced the number of firefighters on the fire ground, we still have a local strike team in place to monitor and respond to any possible flare ups," Mr Costello said.

"Although the fire is contained, a change in weather conditions could see the fire reignite so we are keeping a watchful eye on the ground to monitor any changes."