Apart from metropolitan Adelaide, there is a total fire ban across South Australia due to extreme weather.
Yorke Peninsula and eastern and lower Eyre Peninsula have been given a catastrophic rating, due to the high temperatures and strong winds.
Extra fire crews and water bombers are on standby and 17 state schools and preschools, most on Eyre Peninsula, have been closed for the day.
National parks and reserves also have been closed.
Country Fire Service (CFS) deputy chief officer Andrew Lawson warned people to stay on alert.
"The fuel load is high in many parts of the state and while some areas have not fully cured, fully dried off yet, even though they haven't dried off the fire danger is still extreme and even catastrophic in some areas," he said.
Some Adelaide hills residents and the CFS expressed alarm about a morning burn-off at Aldgate, despite the extreme conditions forecast for the day.
The Adelaide Hills Council gave a permit after clearance work started on Monday afternoon to remove a fire risk.
Mayor Bill Spragg said the council had expected the fire to be out before there was any danger.
"The person started burning off yesterday and there was a risk that the fire was going to continue burning through the night and all we were doing was giving him a permission to allow the fire to burn out," he said.
"It seems that what's happened here is that he's taken, I'd have to say, a liberty in continuing to stack fuel on."
Mr Spragg said the council would now change its permit system to ensure fires were extinguished by midnight ahead of any day with declared fire bans.
By late morning, the CFS stepped in to ensure the Aldgate fire was extinguished.
Chris Martin of the CFS said the owner of the property had cooperated with authorities.
"I've just had a chat with the land owner now and, given the severity of the day, given the severity of the fire weather today, we've decided that it would be prudent to put the heaps out," he said.
The SA Environment Department said most burning off across South Australia was completed long ago.
Chief executive Allan Holmes said 86 per cent of its targeted burn-offs had been completed during autumn.
"We've increased the amount of burning year-on-year for the last 10 years, so in fact the opposite of what's been claimed is occurring. We've increased the amount of fuel reduction burning in the state a very significant amount over the last 10 years," he said.
Domenic Panuccio from the weather bureau said temperatures across SA were heading into the high 30s.
"The hot conditions with very strong winds means that there are very severe fire weather conditions," he warned.
A week ago, a bushfire destroyed property in the Sleaford Bay area and burnt close to the town of Tulka on lower Eyre Peninsula.
Two fire crews were called to the area this morning because of a flare-up from that blaze.
The CFS now says the lower Eyre Peninsula fire was sparked by lightning.
By late morning, crews west of Port Lincoln were tackling another fire.
The bushfire was burning at Coomunga and the CFS said it was a threat to lives and homes.
Fire crews and water bombers were tackling the blaze in scrubland.
The CFS said the fire was burning south towards the Lincoln Conservation Reserve.
Across the state, police patrols are keeping close watch in bushfire-prone areas and police urge anyone who sees any suspicious activity to call them immediately on 131 444.
A cool change is expected to move across SA during the day but will not reach Adelaide and other eastern areas until about evening.
© ABC 2012
17:08 EDT A high pressure ridge cleared skies and a cool air mass created the perfect conditions for temperatures to drop well below the monthly average in parts of New South Wales.