Record-breaking temperatures will continue in southern parts of Australia this week, with Adelaide set to cop the brunt of the heat today.

Temperatures have peaked in the mid-30s in Adelaide and an April heatwave record looks set to be broken in the state capital.

Extreme heat in early April is not abnormal, but with 34 degrees Celsius in Adelaide on Sunday, 35C forecast for today and 33C on Tuesday, a significant record is in danger.

Bureau of Meteorology duty forecaster Matt Bass said South Australia was experiencing temperatures rarely seen at this point of the month.

"Basically we are looking at significant temperatures above average for April across South Australia, southern New South Wales and Victoria in the coming days," he said.

"If we look at Adelaide as an example, it was 34C yesterday, it's forecast to reach 35C today and 33C on Tuesday.

"If we get above 33C today and on Tuesday then it will be the first time Adelaide has ever had three days in a row above 33 degrees in April.

"So that's a pretty significant record there.

"In fact, in parts of southern SA we've even got 40 degrees forecast out at places like Nullarbor and Wudinna."

Beachgoers can expect temperatures in the mid-30s early this week in Adelaide. ( News Video )

Heatwave to move from SA to Victoria

Looking further across southern parts of the country, Mr Bass said the heatwave would continue to test records across the border, with temperatures to soar this week in Victoria and parts of New South Wales.

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"We are forecasting in the coming days that potentially wide parts of Victoria, southern New South Wales and the south-east of South Australia could be reaching record maximum temperatures for April," he said.

"Northern Victoria looks to be reaching the mid to high-30s and the further down you go, you find the low-30s, which is still abnormal for this time of year."

But to those who are looking forward to winter, fear not.

While April should remain fairly warm, a cool change should be expected from Wednesday.

"The heat will hang around on the south-east of the country through until about Friday," Mr Bass said.

"We should see a cool change heading across from Wednesday in South Australia and it should reach southern New South Wales by Saturday.

"That's going to feel a lot more like the winter change we would expect in April."

So where is the heat coming from?

The heatwave is set to continue this week throughout Victoria and southern New South Wales. ( ABC News: Damien Hooper )

Warm air has travelled from Western Australia through to the south-east of the state over the last week, and the trajectory is set to continue.

Mr Bass said the hot air had come from as far as Queensland and the Northern Territory before making its way around to the south.

"The heat has built up across the north and the warm air is coming from Queensland and the Northern Territory, around to WA and down across southern Australia," he said.

"So it's kind of cycling around the country."

Bushfire warning for South Australia

The Bureau of Meteorology has also issued a fire warning for parts of South Australia today.

Hot and dry with north-westerly winds will be increasing to 30 to 45 kilometres per hour over western and central parts of the state during the late morning, then gradually easing during the mid to late afternoon.

Firefighters remain on high alert as they continue to monitor a fire in the Inman Valley on the Fleurieu Peninsula.

Crews remained at the scene overnight after the grass fire burnt through 50 hectares of land on Sunday.

Brett Lachlan, from the Country Fire Service, said unusually hot conditions for April so far following a dry summer made the fire harder to tackle.

"The normal fire danger season ends at the end of this month," he said.