A scorching heatwave is building across the country this week with the Bureau of Meteorology (BoM) forecasting severe and extreme conditions in some areas.

Temperatures are predicted to rise from today in all states except Tasmania, caused by a large high-pressure system moving east across the country from Western Australia.

Severe heatwave conditions are first predicted for the western Top End on Tuesday, rising to severe in some parts on Wednesday.

During this time low intensity heatwave conditions are forecast for across the interior of Western Australia, South Australia and extending into south-western NSW and northern Victoria, becoming severe in SA and WA.

Forecast temperatures: Darwin: 35 degrees Celsius until Sunday

Darwin: 35 degrees Celsius until Sunday Sydney: 33C tomorrow, 38C on Friday

Sydney: 33C tomorrow, 38C on Friday Brisbane: 30C tomorrow, 34C on Saturday

Brisbane: 30C tomorrow, 34C on Saturday Melbourne: 31C today, 34C on Thursday

Melbourne: 31C today, 34C on Thursday Canberra 30-33C from tomorrow to Sunday

Canberra 30-33C from tomorrow to Sunday Adelaide: 34C today, 38C tomorrow

Adelaide: 34C today, 38C tomorrow Perth: 35C on Saturday

By Saturday, large areas of the Top End and the Kimberley are expected to experience severe heatwave conditions.

Low intensity to severe heatwaves are tipped to continue into the weekend in Queensland and north-east NSW, after beginning to rise earlier in the week.

Darwin will be hit the hardest of all the capital cities, receiving temperatures around 35 degrees Celsius until Sunday.

In Sydney temperatures are forecast to reach 33C on Wednesday, peaking at 38C on Friday.

Friday looks to be hottest day in the run with high 30s likely in all suburbs, Weatherzone has reported.

It said there was potential for some places, particularly in western suburbs, to see their first 40C day since last year.

Temperatures in Brisbane will hit 30C on Wednesday and peak at 34C on Saturday, forecasters have predicted.

Melbourne's weather will reach 31C on Tuesday and peak at 34C on Thursday.

Regional areas in both New South Wales and Victoria can expect temperatures in the 40s.

Canberra residents will experience temperatures between 30C and 33C between Wednesday and Friday.

In Adelaide, BoM has forecast 34C on Tuesday, 38C on Wednesday and 35C on Thursday.

Weatherzone said South Australia was on track for its hottest spell since summer and hottest November spell in six years.

Perth is forecast to experience a peak temperature of 35C on Saturday.

The BoM has a live and interactive tool called MetEye where you can see predicted temperatures across the country.