A person has been killed and an unknown number of homes have been destroyed in fires burning throughout South Australia.

Key points: CFS responded to 200 blazes throughout the state

CFS responded to 200 blazes throughout the state A driver died when a car hit a tree near one of the fires

A driver died when a car hit a tree near one of the fires Four firefighters are being treated for burns and smoke inhalation

By Saturday morning, there was only one emergency warning current for "multiple" fires burning on the northern side of Kangaroo Island, near Menzies.

A major fire at Cudlee Creek in the Adelaide Hills, which burned through more than 17,000 hectares, was downgraded to watch and act level around 9:15pm.

However, authorities have said the fire is still uncontrolled.

About 200 blazes broke out in the catastrophic conditions on Friday and authorities confirmed four firefighters were being treated for burns and smoke inhalation.

Three police officers were also injured in a fire south of Adelaide.

South Australian Premier Steven Marshall confirmed a person was killed in a car crash linked to one of the fires in the Murraylands.

Police said a car hit a tree about seven kilometres east of Lameroo, killing the driver, who was the sole occupant.

Mr Marshall said the loss of life was a "tragedy".

In Lobethal, locals took shelter at the town's oval. ( ABC News: Michael Clements )

"It is unclear at this time the exact circumstances of the vehicle collision and the cause of the fire, but they are currently being investigated," SA Police Commissioner Grant Stevens said.

Three Country Fire Service (CFS) vehicles were also destroyed.

Late in the afternoon, SA Water announced that water supply to some parts of the Adelaide Hills, including Lenswood, Lobethal and Woodside, had been affected as fires impacted pumping operations.

"As soon as it is safe for our people to enter the area we will work as quickly and safely as possible to assess our infrastructure and take steps to restore supply," the statement on Facebook read.

"We thought we were going okay but the wood shed caught fire and then that fanned onto the house, and then it was all over red rover, I'm afraid," said Adelaide Hills resident Trevor Kerber.

"Once the wood shed caught hold it was only a matter of a quarter of an hour, and I could see the house was in trouble.

"It was just licking up against the house."

A structure alight in the bushfire at Cudlee Creek, in the Adelaide Hills. ( ABC News )

A giant water bomber from New South Wales was called in to assist ground crews but later had to be grounded due to high winds.

Bureau of Meteorology senior meteorologist Matt Collopy said ahead of Friday evening's change that winds had been recorded "up to 40-50 kilometres per hour, gusting around 80kph".

"We called upon aerial support from New South Wales and Victoria, but, unfortunately, the prevailing weather conditions meant that we couldn't use them for all of this afternoon and they had to be grounded for safety reasons," CFS chief officer Mark Jones said.

"Three CFS vehicles have been burned through."

Kangaroo Island blazes sparked by lightning

Multiple fires burning on the northern side of Kangaroo Island remain at emergency level and could pose a threat to lives and some properties.

The warning is in place for the northern side of Kangaroo Island between Cape Forbin and Emu Bay, including Snelling Beach, King George Beach, Stokes Bay Hummocky Point, White Cliffs, Dashwood Bay, Smith Beach, Wisanger and the Emu Bay township.

CFS said the fires were sparked by lightning earlier in the evening.

Flames engulfed the roof of a home on Woodside Road at Lobethal. ( ABC News: Chris McLoughlin )

Multiple fires downgraded

A fire burning near Coonalpyn in the upper south-east of the state was downgraded to 'watch and act' just before 10:00pm last night.

It burned through around 2,400 hectares of land, according to the CFS.

Firefighters were still concerned the fire may spread into the Carcuma National Park.

"Once more catastrophic conditions have challenged the firefighters of South Australia. We have been called upon to attend over 120 fires at this time today," Mr Jones said.

Cudlee Creek fire continues to burn

The CFS also downgraded the severity of the bushfire at Cudlee Creek in the Adelaide Hills, but firefighters said conditions were continually changing and the bushfire was still a threat.

The Cudlee Creek fire broke out on Friday morning, putting multiple townships and structures under threat.

The warning area includes Mount Pleasant, Springton, Palmer, Cudlee Creek, Mount Torrens, Harrogate, Inglewood, Gumeracha, Lobethal and Woodside.

This scrub fire is burning in a north/north-easterly direction towards Cudlee Creek, Mount Torrens, Harrogate, Gumeracha, Inglewood, Chain of Ponds, Houghton, Paracombe and Birdwood and conditions are continually changing.

Members of the public have been advised to avoid the area.

Annie Whicker walked her horse Silvah from Woodside to Balhannah to escape the Cudlee Creek blaze. ( ABC News: Patrick Martin )

Early on Friday afternoon, Woodside resident Annie Whicker spoke to the ABC from Balhannah Oval, after walking there from Woodside with her horse to escape the Cudlee Creek blaze.

When Ms Whicker next spoke to the ABC on Friday evening, she had found out that she had "lost everything".

"Our property is gone, the fires went through and have taken it all," she said.

"My husband and I are here with our horse, and my daughter is here, who we have been separated from all day — so it's nice to be back together, to have some of the family here.

"The community here, since we've been here this morning and all day, we all had hopes and we all had different stories — 'your house is safe … but it burned your neighbours' — then the news came through that ours had gone as well.

"So you feel like at least you're not alone, because so many people have lost so much today.

"A beautiful couple in there, I was speaking to earlier from Lobethal, lost their home, and his business. We run our business from home, so all our business paperwork is gone, but we're all alive and we'll have to regroup and get it together.

Thick smoke from the Cudlee Creek bushfire can be seen from the main street of Lobethal. ( ABC News: Chris McLoughlin )

"But it's really cruel … it's still cruel to lose everything, everybody within their own property works so hard on their properties and to see it turn to ash is so difficult."

There are reports local wineries were also impacted by the fire.

Fires at Maitland, Virginia and Parilla were downgraded on Friday afternoon after all earlier reaching the highest threat level.

A fire burning in Adelaide's north was also contained and downgraded to a watch and act for residents in Hillier, Hillier Park, Munno Para Downs, Kudla, Munno Para West and Angle Vale near Gawler.

Cool change swept through following heatwave

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The catastrophic fire conditions for much of the state came during a fourth day of extreme heat.

Adelaide reached 43.9 degrees Celsius after an earlier forecast of 46C following the hottest night on record at the West Terrace weather station.

Temperatures throughout regional South Australia soared into the mid to high 40s, with Keith reaching 49.2C.

More than 450 people have suffered from heat-related illnesses so far this week.

Heat-related illness resulted in 65 people being taken to hospital on Friday.

SA Health said it was managing demand and had freed up capacity by safely discharging patients and cancelling elective surgeries.

It said there had been an increase of heatstroke and cardiac-related issues with at least eight people suffering burns or smoke inhalation in Friday's fire emergencies.