Muchof NSW is set to endure another sweltering day as Sydney's west heads for a third consecutive maximum of 40C, with the mercury set to hit 47C in the state's outback.

In northern Victoria, heatwave conditions continue with 17 major centres expected to endure a high of at least 40 degrees on Sunday.

A relatively mild Brisbane should see 30C on Sunday, Canberra and Adelaide an uncomfortable 36C and Perth 33C. Hobart will be the coolest on Sunday reaching just 24C.

Residents in Penrith, in Sydney's west, will have to deal with at least 40C on Sunday and then a blistering top of 43C on Monday with conditions only easing slightly through the week into the mid 30s.


Residents in Ivanhoe will face temperatures of 46C on Sunday, as will those in the nearby town of Menindee and the Riverina town of Hay. Wilcannia in the far west is bracing for 47C.

However, Sydney's CBD will escape the heat. Aided by cooling sea breezes the mercury is unlikely to push north of 30C.

Most NSW regions are likely to remain hot for the remainder of the weekend, with as many as 30 western and northern centres forecast to top 40 degrees. Firefighters are keeping a close eye on bushfires across the state with four regions — the Southern Ranges, Central Ranges, Greater Hunter and North Western- subject to total fire bans on Sunday.

NSW Police has reminded motorists it's not only an offence for children or pets to be left unattended in a vehicle, but it can be deadly.

Drivers are also reminded to keep an eye on elderly and disabled members of the community in cars during days of extreme heat.

"Everyone needs to take care in hot weather, but some people are at higher risk of heat illness, especially if they are older, live alone or are socially- isolated," a NSW Police spokesman said.

South of the border. Mildura and Swan Hill in the Mallee will bear the brunt of a 44C day as will Yarrawonga and Cobram on the NSW border.

Wangaratta, Rutherglen, Shepparton and Echuca will fair scarcely better with forecast tops of 43C.


In stark contrast, Melbourne, Geelong and much of the state's south can look forward to temperatures in the mid 20 to low 30s and isolated showers before the swelter returns next weekend.

A severe fire danger warning and total fire ban continues for the Mallee, according to the Bureau of Meteorology with high to very high warning levels in effect elsewhere in the north and reducing to moderate in the southwest. The bureau expects extreme heatwave conditions to contract out of Victoria towards Monday but hang around in southern NSW.

"There's not really any relief during Sunday, however on Monday we do have southerly winds freshening a little," senior forecaster Michael Efron told AAP on Saturday.

The consistent heat across the state has had a wideranging impact for emergency authorities.

Fire crews have battled hard with two large, remote fires in the Big Desert area near the South Australian Border.

An 80-hectare fire at Smeaton, northwest of Melbourne, was brought under control on Saturday afternoon by crews manning 30 tankers and several aircraft. Health authorities continue to urge people to stay hydrated, make sure children and pets are not left in cars, to check in on others and stay cool.

The Australian Veterinary Association has warned farmers to take measures to protect livestock in the extreme heat.

AVA President Dr Paula Parker says livestock and horse owners should ensure water supply is high.