At least four houses have been destroyed by a bushfire in the Adelaide Hills that is burning at Humbug Scrub near Kersbrook, north-east of the city.

The fire was one of two that South Australian firefighters said had threatened lives and homes on Friday as temperatures across the state soared into the mid 40s.

Country Fire Service spokesman Brenton Eden said it was unclear if anyone had been injured in the fire, which started at Sampson Flat earlier on Friday.

"I can confirm that we have lost four houses," Mr Eden said.

"It appears two houses belonged to members of the CFS which is quite tragic that they're out there fighting fires and have lost their own properties."

Mr Eden warned residents to be aware of an expected wind change over Friday night.

Metropolitan Fire Service crews joined CFS volunteers who were engaged in asset protection in the area.

The remains of a house destroyed by fire near Humbug Scrub. ( ABC: Alina Eacott )

Mr Eden said an incinerator was the likely cause of the fire, which has also destroyed a firefighting appliance, but no-one was hurt.

He said 150 firefighters, 25 appliances and five water carriers were at the scene and communities around the fire including Kersbrook, Humbug Scrub, Birdwood and Gumeracha needed to be "very, very vigilant."

The fire has already blackened 1,600 hectares.

Swirling winds were making conditions difficult and CFS incident controller Robert Styling said firefighters were working to protect properties.

"They're engaged in asset protection at the moment because there are a number of small farm lots and homes in and around the fire danger area and also the township of Kersbrook is of some concern to us as well," he said.

"The fire is still completely out of control on a number of fronts."

Smoke from a fire at Humbug Scrub is seen rising above Cudlee Creek in the Adelaide Hills. ( Supplied: Geoff Fulwood )

Mr Styling said firefighters who have been battling the blaze for eight hours would be relieved by other crews who have a tough night ahead of them.

"Oncoming weather conditions are not going to be very kind to us at all overnight," he said.

"We're not expecting the temperature to drop between 30C and 32C right through the night and the wind is going to be up around 40 kilometres an hour."

Roads around Kersbrook have been blocked off around the fire, while some not far from the area have already fled their homes because of embers.

Smoke from the fire at Humbug Scrub was earlier visible above Adelaide suburbs as far away as Unley and at Echunga, more than 25 kilometres away.

Fire burning out of control in vegetation at Tantanoola

The CFS said a second out-of-control fire in thick vegetation in South Australia's lower south-east had been slowed.

Water bombers from Victoria and New South Wales were called in to help fight the fire near Tantanoola and Glencoe in the lower south-east, which had burnt around 500 hectares.

Large air-tankers from Victoria known as LATs were used for the first time in South Australia.

"They've come in to give us quite a considerable bulk load of retardant. 11,500 litres they're dropping," Mr Eden said.

Mr Eden said 175 crews would be working to protect the communities of Glencoe and Wandilo over Friday night.

"We've deployed two of our state incident management teams with one on standby so these fires are heavily resourced and they will be for days to come."

Large plumes of smoke from both fires were visible for miles around, with strong winds fanning the flames.

A section of Princes Highway had been closed.

"In that particular area there are quite a number of pine forests," CFS Chief Officer Greg Nettleton said.

"We've got a number of resources, both air and land, combatting that fire to prevent it from getting into pine forests and then spreading further afield.

"There are also a number of eucalypt forests down in that area."

The cause of the fire was not known.

Adelaide reaches 44C, Ceduna 46C as CFS looks to Saturday

Adelaide reached 44.1 degrees Celsius on Friday, more than two degrees above the forecast top, and it was even hotter in Ceduna where it reached 46C.

Real-time wind map of Australia

Total fire bans were current for 14 of the state's 15 districts and the CFS said the fire threat would continue on Saturday, with bans in 13 districts.

The weather bureau has forecast temperatures ranging from the high 30s to low 40s across South Australia ahead of a change that is expected to bring thunderstorms.

Senior forecaster Vince Rowland said strong wind ahead of a trough would combine with lightning strikes to create more dangerous fire conditions, especially inland.

"We will be looking at increased fire dangers again so people should certainly be aware," he said.

"Overnight we'll get a bit of an easing of the wind but certainly tomorrow [Saturday] again ahead of the trough, we'll see those northerlies pick up again."

CFS assistant chief officer Rob Sandford said while crews remain preoccupied by today's fires, planning was underway for Saturday.

"Our crews have done an outstanding job," he said.

"We need the entire community to be prepared for the rest of today, through tonight and through tomorrow because the conditions tomorrow could see that we have fires that again may threaten communities across the state."

"The Bureau of Meteorology have advice that we could see lightning across most of the state on Saturday.

"We want people to be vigilant. If they see an unattended fire, we want them to report it immediately."

South Australia experienced a dry end to winter and received very little rain throughout spring, experiencing its hottest October on record.

The result is a high fuel load of dry undergrowth and grasses.

Fire bans must be observed, CFS says

Mr Sandford warned people to observe the total fire bans.

"If you cause a fire to be lit during the fire danger season, it is likely you'll receive some sort of penalty as a result of that," he said.

MFS assistant chief fire officer Paul Fletcher said it was important household air conditioners were serviced.

"We've had 24 house fires caused by overheating and electrical cooling equipment and we don't want any more," he said.

Animated map: Track temperatures across Australia Track the weather across the country with our animated visualisation of temperatures over the past seven days - updated hourly.

"We observe householders to take note of these tips, combine that with a working smoke alarm and also have yourselves an evacuation plan to get out of the house in case of fire."

National parks closed on Friday included Cleland Wildlife Park and Mount Lofty Summit in the Adelaide Hills, and the Naracoorte and Tantanoola Caves in the south-east.

Tram services were disrupted because of a breakdown on the line on Port Road outside the city.

Passengers were forced to walk about two kilometres from West Terrace to the Entertainment Centre in the hottest part of the day.

"There wasn't much information. The guy just said 'get off and make your own way'," one passenger said.

"It's a stinking hot today. I think it's 42 degrees. You're sweating like crazy carrying the shopping bags.

"There's a lady who's walking, we passed on the side of the road. She was on the tram, she's pushing two kids in a pram. It's probably not the best thing for her kids to be out in such heat."