The State Emergency Service on Monday issued severe heatwave warnings for the Riverland, Murrylands, West Coast, and North West Pastoral regions, with a low intensity heatwave warning for much of the rest of South Australia including the Adelaide metropolitan area.

Heatwave warnings have also been been issued for Western Australia, Victoria and Tasmania with temperatures 8C to 16C above average.

Meanwhile, Melbourne expects a top of 37C for day two of the Boxing Day Test while most of Tasmania, including Hobart, is due to rise to more than 30C.

Canberra will also see the mercury surpass 30C after dipping to 11C overnight and Perth can expect a high of 27C.

Much of inland NSW is headed for maximums between 35C and 40C but coastal breezes will keep Sydney to about 28C.

While some welcome sweltering conditions, severe heatwaves can be dangerous, particularly for older people, babies, children and pregnant and breastfeeding women.

The Bureau of Meteorology advises people to seek a place to keep cool, such as a home, a library, a community centre or a shopping centre.

Heatwave conditions are expected to ease on Wednesday and Thursday following a cool change.

Further north, a severe weather warning remains in place for the Northern Territory across parts of the Barkly and Simpson districts.

The slowly moving ex-tropical cyclone Ellie is bringing rainfalls totalling up to 300mm for some areas east of Tennant Creek, raising concerns of flash flooding.

Kalkarindji on the Buntine Highway copped 60 millimetres of rain in 30 minutes to 1.32am on Tuesday.

“Although the system is forecast to temporarily weaken today, heavy rainfall and thunderstorm activity is expected to continue,” a BoM statement said.

-with AAP