NSW could experience its hottest February day on record this weekend with emergency services staying on high alert for catastrophic fire conditions.

A state-wide total fire ban has been declared for Saturday as the mercury soars past 40C.

"If you're a little bit inland from the coast in Sydney or the Hunter district, you'll experience probably mid-40s," senior forecaster at the Bureau of Meteorology Andrew Haigh told AAP.

"That goes for anywhere west of the ranges as well".

The state's northwest will cop the brunt of the extreme heat with Wilcannia, Ivanhoe, Bourke and Menindee forecast to reach 47C on Saturday.

In the Hunter region, Singleton and Cessnock are predicted to reach 46C and 43C on Sunday.

The Rural Fire Service has warned of a potential "catastrophic" fire danger warning on Sunday largely around the Hunter, from the coast, mid-north coast, out through the Central Tablelands, the top end of the greater Sydney region and out to the central west.

The RFS has urged residents to have their bushfire survival plans ready.

The sizzling conditions will also continue to push the state's energy network to limit with demand for power among the highest on record.

NSW managed to dodge widespread power blackouts on Friday despite demand reaching unprecedented levels as temperatures reached 45C in western Sydney and 47.4C in the western Riverina town of Hay.

The stress on the system will persist over the weekend, the Australian Market Energy Operator says, and it's warned residents to be mindful of their electricity use.

Sydney will get no relief over the weekend with the city forecast to reach 39C on Saturday, and the west to reach the mid-40s.

The state's Forestry Corporation has closed all forests between Sydney and Kempsey in the state's north, along with forests in the Pilliga region and the Talleganda State Forest on the Southern Tablelands.

Saturday's Randwick races have been postponed to Monday due to concerns about the welfare of horses and riders.

Newcastle's A-League soccer match against Melbourne Victory has also been postponed until Monday, while Football NSW has cancelled all Saturday trial games for under-18s and below and shifted under-20s and first grade trials to evening start times.

NSW's three NRL trial matches will however go ahead on Saturday evening, as will the Sheffield Shield clash between NSW and Queensland. Cricket NSW has cancelled all grades of Premier Cricket, while most school and children's sport has been cancelled.

With many people heading to waterways to cool off in the heat, parents are being urged to keep an eye on children following a tragic summer of drownings.

Health experts are reminding people to stay hydrated, wear sunscreen and look out for people most at risk, while NSW clubs say they will provide water and respite for vulnerable people.

Victoria

People in Victoria's north have to suffer through one more day of 40 degrees Celsius plus heat before a cool change brings relief.

Temperatures have been scorching for residents in Mildura, who contended with a sticky night before the mercury reached a top of 46 degree.

Relief isn't in sight yet, with the weather bureau predicting the border town will reach a top of 43 degrees today.

Queensland

A heatwave sweeping southern Queensland, which will push temperatures past 40C, has paramedics on high alert.
Heat records could tumble over the weekend, with the state's hottest February day a possibility of being broken.

The weather bureau is forecasting temperatures in the mid-40s in the state's southwest and a top of 36C in Brisbane on Saturday.

The heat will crank up again on Sunday, with a maximum of 39C forecast for the capital.

The mercury is expected to reach 46C in Birdsville on Saturday and Sunday, nudging the town's February heat record of 46.2C and the Queensland record of 46.5C.

The sweltering conditions are set to push temperatures 10C past the February average, with paramedics urging people to keep hydrated to avoid becoming ill.

They've suggested swapping caffeinated drinks for water, eating small and regular meals and wearing light-coloured cotton clothing.

"Heat-related illnesses have the potential to be life-threatening and may include heat stroke," Queensland Ambulance Service spokesman Lachlan Parker said.

Those planning to crank-up the air-conditioning have been assured they can rely on Queensland's power network, which was used to help NSW meet its power needs on Friday.

"We have confidence in the Queensland power system, which is very robust," Queensland Energy Minister Mark Bailey said.