Bushfires currently burning in South Australia could break containment lines, putting residents at higher risk, during another wave of extreme heat which will cross the state on Friday.

Key points: The CFS says it is particularly concerned about the fire situation on Kangaroo Island

The CFS says it is particularly concerned about the fire situation on Kangaroo Island Fires could break containment lines as winds strengthen and temperatures rise above 40C

Fires could break containment lines as winds strengthen and temperatures rise above 40C The CFS has urged people near existing fire grounds to enact their bushfire survival plans

As eastern Australia's fire crisis deepens, severe to extreme fire danger has been declared in nine districts across SA, and temperatures in the mid-40s will be accompanied by hot northerly winds, ahead of a gusty change with possible lightning.

The County Fire Service (CFS) is currently battling several fires of concern, including at Ravine on Kangaroo Island, where more than 9,000 hectares of scrub and vegetation have been blackened.

A fire at Keilira in the state's south-east has destroyed three homes, while a blaze which caused widespread blackouts on Eyre Peninsula has burnt through 11,500 hectares at Miltalie.

"If you live near any existing fires, you need to enact your bushfire survival plan as these fires may increase in ferocity," CFS chief officer Mark Jones said yesterday.

"We're particularly concerned about the communities and travellers on Kangaroo Island, with two fires burning [there].

"The fire conditions that we have, with a prolonged drought and very dry vegetation which is ready to burn — there's a chance of very rapid fire spread."

There are concerns homes on Kangaroo Island have been lost after two fires merged near the Ravine Des Casoars Wilderness Protection Area.

"We anticipate that it will move in a southerly to south-easterly direction … if it breaks containment lines," Mr Jones said.

The fireground is not far from another at Duncan, where a blaze was contained on Tuesday.

The burnt remains of a ute at De Mole River on Kangaroo Island. ( Supplied: Alison Alcock )

Poor mobile phone coverage on the island has made it difficult for volunteer firefighters to communicate, local MP Leon Bignell said.

However, 20 two-way radio sets were secured after a call was put out on social media.

"If you're holidaying over there, be vigilant again and make sure you know what is happening in your localised area," Emergency Services Minister Corey Wingard said.

Main focus on containment, CFS says

Adelaide is heading for a top of 42 degrees Celsius on Friday, with even hotter temperatures inland, including 45C at Renmark and Roseworthy, 46C at Port Augusta and Wudinna and 47C at Oodnadatta and Tarcoola.

"Temperatures will significantly increase across the state … with dry northerly winds strengthening," meteorologist Jon Fisher said.

"Even with that south-westerly change — it will be a fairly strong and gusty south-westerly change as it moves across the state — that does bring a risky period in terms of fire weather."

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Extreme fire danger has been declared for the West Coast, Lower Eyre Peninsula, Mount Lofty Ranges, Yorke Peninsula, Kangaroo Island and Lower South East districts.

Severe Fire Danger is forecast for the Eastern Eyre Peninsula, the Mid North and the Murraylands.

The CFS said while the fire danger index was not as elevated as the day the Cudlee Creek fire started in catastrophic conditions two weeks ago, the situation was now different.

"We have a number of fires which are burning which we didn't have on that day which are likely to break out. The ignition sources are already there on this occasion," Mr Jones said.

"The main emphasis will be on containing the fires which are currently burning.

"If they do break out, the mission turns to making sure the people in harm's way are safe."

Arsonists have also been warned, after a fire which came close to a campground at Rapid Bay earlier this week was declared suspicious.

"If anyone out there sees or knows anything I call on them to contact police straight away, it's stupid and it's not to be tolerated and we need to act as swiftly as possible when we find these people," Mr Wingard said.

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Watch Duration: 36 seconds 36 s Witness John Koutrikas took this video of the fire at Rapid Bay.

On Thursday, victims of the deadly Cudlee Creek fire in the Adelaide Hills were invited to attend a State Government-organised meeting at Hahndorf to discuss rebuilding options.

Primary Industries Minister Tim Whetstone said the economic cost of the fires could reach $100 million.

"We're talking about 1,200 hectares of vineyard which have been damaged," he said.