Fire destroys a house at Rockleigh, near Monarto, south of Adelaide on Tuesday, January 14. Video supplied.

FRIDAY will be the real bushfire danger day in South Australia, the CFS has warned, even though Adelaide is officially the hottest city in the world today.

The maximum temperature so far in Adelaide is 44.2C at 3pm, although it has been several degrees warmer in the northern suburbs.

The temperature in Roseworthy, north of Adelaide, hit 46.4C at 1.58pm.

Adelaide has now recorded three consecutive days above 43.5C for the first time.

However, we've been neck and neck with Melbourne, which has today maxed out at 43.9C.

Adelaide's forecast top for Friday has been revised up to 42C after an overnight minimum of 31C - but increasing winds will make fire conditions the most dangerous so far during this heatwave.

Country Fire Service chief officer Greg Nettleton said Friday would be extremely perilous for firefighters and a total fire ban would be declared across the state.

Twelve of the 15 fire ban districts have been rated as severe, while the Mt Lofty Ranges, Upper South East and Lower South East are considered extreme fire dangers.

Mr Nettleton said the three main bushfires were burning in the Yumbarra Conservation Park at Ceduna, Ngarkat Conservation Park in the state's Upper South East and the Gawler Ranges.

"We are going into an escalating fire pattern over the next 48 hours," he said.

"At this stage we are confident that we have got sufficient resources to deal with the current situation, however it could change quite rapidly, particularly when the hotter weather and the winds come through.

"The real concern and what really puts up the fire danger rating is wind and we are seeing wind starting to come through tomorrow."

Mr Nettleton urged people to ensure they had a bushfire survival plan.

Bureau of Meteorology acting regional director John Nairn said increased wind speeds and lightning would increase the bushfire risks.

Mr Nairn said a cool change would not reach Adelaide until late on Friday.

"Once that change moves through we will see southerly winds come in and they will freshen and they will be more humid ... rising humidity will eventually moisten the fuels so the fuels won't burn as fast, but that won't happen for a while because they won't be able to absorb the moisture quickly enough," he said.

Load shedding - or rolling blackouts at times of peak power demand - is now unlikely to occur, although several thousand houses around the state did lose their power supply this afternoon.

MORE: For the latest power outages, click here.

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ADELAIDE'S TEMPERATURE HOUR-BY-HOUR SINCE MIDNIGHT

5pm - 43.4C

4pm - 43C

3pm - 44.2C

2pm - 43.1C

1pm - 42.4C

Noon - 42.1C

11am - 40.7C

10am - 38.6C

9am - 37.4C

8am - 34.9C

7am - 30.9C

6am - 30.8C

5am - 32.2C

4am - 34.1C

3am - 33.8C

2am - 35.1C

1am - 36.4C

Midnight - 35.3C

Premier Jay Weatherill said the lack of relief from the heatwave would take its toll.

Mr Weatherill urged people not to venture out into the extreme heat even if they felt like they had been confined to their home.

"We may be reaching quite a dangerous phase in this heatwave and it is important that people are well aware of those risks," he said.

"Just because we are appear to be getting closer to some of the cooler weather does not mean that the threat is receding. If anything, the threat is increasing.

"Don't be too proud to ask someone for help. If people are feeling overwhelmed they should not hesitate to contact the authorities."

There have so far been no reported deaths from the heatwave but there have been a total of 163 heat-related hospital admission across South Australia since Monday.

As of 4pm there had been a total of 34 presentations to metropolitan Adelaide hospitals today.

SA Health chief public officer Dr Stephen Christley warned it was very likely that the heat would contribute to some deaths among the elderly and frail.

SA Health and the SA Ambulance Service have both increased staff numbers to deal with the expected rise in demand, with ambulance services experiencing a 20 per cent rise in demand.

Health officials are urging the public to take particular care of the elderly, vulnerable and people with chronic conditions such as heart conditions during the heatwave. They also are warning people to beware of sunburn which can occur rapidly in the intense conditions.

Gathering official predictions from around the globe, the United Nation's World Meteorological Organisation estimated Adelaide would be the hottest major population centre on Earth today.

Only other Australian cities were predicted to come close to Adelaide's top, with Canberra expected to reach 40C, Melbourne 44C and Mt Gambier 45C.

Meanwhile, South American capitals, also deep into summer, are experiencing much cooler conditions except in Brazil where Rio de Janeiro is expected to reach 40C overnight (Adelaide time) and then 34C on Thursday.

Santiago in Chile is predicted to be 34C, Buenos Aires in Argentina will be 35C.

New Zealand cities were all predicted to only reach the mid-twenties.

Normally home to most of the hottest cities on Earth, the northern hemisphere is in the grip of winter, and southern hemisphere cities are not expected to come close to Adelaide's extreme heat.

Even Bangkok, Thailand, ranked the seventh hottest city in the world for average temperatures, will experience a comfy 32C on Thursday.

The prediction coincides with the release of interim findings of the Climate Council's new report, Australian Heatwaves: Hotter, Longer, Earlier and More Often.

Report author Professor Will Steffen said it was clear that climate change "is making heatwaves more frequent and severe".

"Heatwaves have become hotter and longer, and they are starting earlier in the season," he said.

"Australia has always had hot weather. However, climate change is loading the dice toward more extreme hot weather."

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