As South Australian firefighters continue to battle blazes that broke out during catastrophic conditions on Monday, a suspicious grassfire has come close to a popular camping area south of Adelaide.

Key points: Temperatures reached the mid-40s in some parts of the state on Monday

Temperatures reached the mid-40s in some parts of the state on Monday A bushfire at Keilira has burned through about 25,000 hectares

A bushfire at Keilira has burned through about 25,000 hectares The CFS says it believes a number of properties have been lost at Keilira

The fire, at Second Valley on the Fleurieu Peninsula south of Adelaide, was an unwelcome sight to campers as it burned in hills overlooking the Rapid Bay caravan park.

"I saw flames going up the hill, and it was on the ground as well. It was really daunting," local resident Anika Wollaston said.

"The campground is pretty much full, and many campers were looking at the blaze.

"A lot of campers were just packing up and leaving."

The Country Fire Service (CFS) earlier issued a watch and act message, before it was downgraded and police are now the treating the fire as deliberately lit.

A fire has come close to the Rapid Bay campground on the Fleurieu Peninsula. ( Facebook: Ahlia Olley )

Water bombers were called to assist firefighters and 10 appliances on the ground.

Nearly 40,000 hectares have burned across the state over the past 24 hours, with several bushfires yet to be controlled.

A blaze at Ravine in Kangaroo Island has sent smoke across the Adelaide sky, with the Bureau of Meteorology expecting the haze to continue into tomorrow.

A watch and act message remains in place for that fire in the island's north-west.

For the first time since breaking out more than 11 days ago, the deadly Cudlee Creek fire in the Adelaide Hills has been declared contained but remains at advice level.

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The CFS said smouldering tree stumps would likely cause flare-ups over the coming weeks.

It offered a "huge thankyou" to volunteers who responded to the emergency.

"Volunteers and staff will continue to work on this fire by patrolling, checking, planning and extinguishing, up until the fire is able to be declared complete," it said.

"The community response to this fire has been exceptional."

Authorities have begun to assess the full damage of Monday's catastrophic conditions.

At least three homes have been destroyed by a bushfire which also killed thousands of livestock and burned through almost 25,000 hectares at Keilira in the state's south-east.

Local resident Phil Clarke returned to inspect the remains of his property at nearby Bin Bin on Tuesday.

Mr Clarke was fighting the fire at its ignition point on Monday when the wind changed direction, putting his wife Anthea and their home in the firing line.

He said he made a frantic call over the radio to warn her.

"I said, 'Just grab a bag mate or don't even grab it, just go with what's on you' and she said, 'OK'. I was yelling, 'Just go, go, go,'" he said.

"I had to drive through 6 kilometres of flames with the trees each side burning, I didn't know if I was going to get there or not."

CFS officers and volunteers pick up debris from the road following strong winds and fires in SA. ( ABC News: Stacey Lee )

While Mr Clarke and his wife managed to escape the inferno, their home of more than 18 years was destroyed, and Mr Clarke said he had lost "everything".

"Eight hundred bales of hay, the lads are going through the sheep and cattle to see what we've lost, probably 40 kilometres of fence and the house," he said.

Properties lost but many more saved, CFS says

Incident controller at the Keilira bushfire, Richard De Groot, said the fire had a perimeter of more than 80 kilometres.

"I can say that we understand there are three structures that have been impacted, but we don't know the makeup of [those]," he said.

Scrubland burns at Keilira, in the south-east of SA. ( Supplied: CFS )

He said while some properties were damaged, firefighters should be applauded for their work to save many more.

"What I can say is yesterday the firefighters made some excellent saves, I understand over 20 properties were being impacted on and as a result of our firefighters they were protected or saved," he said.

South Australian MP Nick McBride, who is the local member for Mackillop in the south-east, said he had also heard of three properties damaged by the Keilira fire, and countless livestock had been killed.

Firefighters swiftly got on top of several flare-ups. ( ABC News: Stacey Lee )

He said the Keilira fire had devastated prime cropping land, with farmers beginning the grim task of euthanising injured animals.

"Infrastructure-wise, I'm hearing two or three haysheds which were full, I'm hearing at least three houses have been lost, no lives and look this is very early days," he told ABC Radio Adelaide.

"We're hearing severe stock losses … we're talking thousands.

"A lot of that is the euthanising of stock and destroying and cleaning up."

He said many producers were caught out by the wind change that came through on Monday, which changed the direction of the fire.

"Some large grazing properties have been really, severely affected," he said.

"It burned out, I'm hearing nearly 95 per cent of property on the northern side of Keilira because of the wind change from a northerly direction to a westerly and blew the fire to the east.

"People had put their stock up out of the way of the fire coming in a southerly direction and it's basically cooked a lot of stock and caused a lot of misfortune for a lot of farmers up in this area."

A lightning strike over Sheringa, on South Australia's Eyre Peninsula. ( Supplied: @samanthalodgephotography/Instagram )

Fires fanned by strong winds on Monday also caused power outages for thousands of customers on the Eyre Peninsula, with power restored just before midnight.

CFS chief officer Mark Jones on Monday said the south-east fire had run through a large area of grassland.

"It is believed to have been caused by a dry lightning strike and is running through scrub and grassland," he said.

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Watch Duration: 32 seconds 32 s ABC News reporter Brittany Evins captured this footage of a dust storm while driving back to Adelaide from the Riverland.

'Pretty challenging weather conditions'

CFS communications officer Brett Williamson this morning said firefighters were challenged by the extreme conditions on Monday, all across the state.

"Yesterday presented some pretty challenging weather conditions for us with the heat and wind that changed direction throughout the day," he said.

"At around 6:30pm last night we had attended 154 different incidents across the state, we had 135 fire trucks active on firegrounds with about 540 CFS personnel."

CFS crews take some downtime amid the Cudlee Creek bushfire in the Adelaide Hills. ( ABC News: Catherine Zengerer )

Cooler weather is expected to help firefighters control bushfires burning across the state over the next two days, with forecast temperatures in the mid-20s.

However, the CFS is concerned ahead of another day of hot and windy conditions on Friday, which is forecast to rise above 40C.

"Conditions are better for us today, so now will be the time where we really do try and make some headway and be able to get some better ground covered on some of these fires before the heat returns on Friday," he said.

"It's been a really tough couple of weeks for our volunteer crews and they've done a fantastic job over, particularly the last 24 hours, to make sure that all their work is paid off and none of these fires that were already existing jumped out."