Large parts of Australia to swelter, NSW on alert for its hottest day in ...

New South Wales is sweltering under a "severe" heatwave today, while large parts of the rest of Australia are also feeling the summer sun in full force.

By 10:30am temperatures in Sydney had already soared to 35 degrees, with the expected peak of 44 for Sydney's west still hours away.

By 1pm temperatures had officially cracked 40 degrees in most of the city, with scattered power outages detected around Sydney.

It was 22 degrees in Sydney's Observatory Hill by 6am this morning, with most of the state experiencing a "severe" heatwave, according to the Bureau of Meteorology.

By 11:30, Penrith and Richmond in the city's west had reached 40 degrees, the current hottest part of the city.

Soon, the rest of the city joined the west with temperatures sitting at 43 degrees at Sydney Airport.

Around 1 pm, Penrith and Richmond were both above 42 degrees.

Many parts of the state were expected to eventually reach 8-10 degrees above their average, the Bureau said.

"The heat spreads right out across the majority of NSW all the way down the coastline with a lot of interior places somewhere between 40 and 45 degrees," Bureau of Meteorology spokesperson Angus Hines told Weekend Today.

"The past couple of days we have seen a few weather stations around 46, so we couldn't rule that out for today."

A low pressure system is gradually moving across the country from the southwest, having already passed over Adelaide, Melbourne and Hobart.

But with that cool change comes another danger.

A vigorous southerly wind change will move rapidly northwards along the coast during this evening, the Bureau of Meteorology said.

"Damaging winds averaging 60 to 70 km/h with peak gusts in excess of 90 km/h are possible along parts of the Illawarra and Sydney coastline this evening," the weather bureau said.

The heatwave in NSW will give way to cooler temperatures on Sunday.

In the meantime, crowds packed out the popular beaches across Sydney, with tens of thousands of people expected to hit the surf at Bondi today.

During times of extreme heat, the state's electricity network can take a beating as homes and businesses crank the air conditioning.

This can lead to blackouts due to the high demand.

Some "unplanned" power outages were reported across Sydney with residents in Auburn, Hornsby, and Avalon affected.

Scattered power outages across Sydney were detected on Ausgrid's outage map.

Ausgrid said that the outages were due to unknown causes.

Nearly 1200 customers were affected by an unplanned outage in suburbs around Auburn.

Several other smaller unplanned outages were detected, with dozens of homes disconnected.

Ausgrid has been approached for comment.

It is not yet clear if the outages were due to problems within the grid.

The rest of the city's grid was mostly unaffected by blackouts.

There are also concerns that the extreme heat will fuel over 20 bushfires currently burning uncontained across the state, with another 28 being controlled by the Rural Fire Service.

"Total fire bans are in place whilst we see through this extraordinary hot weather, but coupled with some very dry humidity and also strong winds today... it is going to be a testing [day] today," RFS spokesperson Ben Shepherd said.

"We are in a reasonable position but we would ask the community to be vigilant, report any new fires to 000 immediately because we need to get to them as soon as possible to keep them as small as possible." 

Meanwhile, festival-goers are gearing up for the hardstyle rave, Epik by Events HSU, with extensive measures being put into place to keep ravers safe in the heat.

"We have been working with NSW Health who have recommended you start drinking lots of water electrolytes from tomorrow," event organisers said yesterday.

"We will go above and beyond to keep this a great experience, but please know your limits, especially in this heat."

Residents would have felt the heat overnight with intense humidity making it feel like 26.7 degrees in Canterbury and 25.1 degrees at Observatory Hill by 1 am. 

Earlier forecasts showed that humidity is set to make temperatures feel even higher, as the mercury climbs 15 degrees above the December average and delivers the hottest day in almost four years.

Penrith last reached 44 degrees in February 2020 and Sydney's last hottest day was in November 2020, when the mercury reached 39 degrees.

In other parts of NSW, temperatures last reached the mid-40s in December 2020 in Tamworth and Dubbo, while November 2020 saw Wollongong and Gosford record top temperatures of 39 degrees and 41 degrees, respectively.

To combat today's temperatures, Lord Mayor Clover Moore announced that all six of the City of Sydney's public pools will be free to visit.

The ACT is forecast to reach 37 degrees today.

There is a total fire ban across Greater Sydney, Lower Central West Plains, Southern Slopes, Northern Riverina and Central Ranges areas.

The NSW Rural Fire Service is warning of "very hot, dry and windy conditions".

"We're going to see 30-40km/h winds most likely and that's gonna make it a really challenging day should fire start," Deputy Commissioner Peter McKechnie said.

A severe heatwave warning is also in place for parts of Queensland, with the Bureau of Meteorology forecasting "maximum temperatures in the mid to high 30s, increasing to the low to mid 40s over inland Queensland".

"Overnight minimum temperatures in the mid to high 20s," the bureau said.

The weather warning extends until Monday and covers the Peninsula, Gulf Country, North Tropical Coast and Tablelands, Channel Country, Maranoa and Warrego and Darling Downs and Granite Belt regions.

Brisbane is set to be a little cooler, with highs of 30 degrees forecast.

However the entire country will not be experiencing a heatwave, with a strong cold front pushing across south-eastern Australia.

According to Weatherzone, the weather system will bring a stark contrast in temperatures, with Melbourne to be about 25 degrees cooler than Sydney, with highs of 19 degrees.

Adelaide is forecast to reach only 17 degrees, while Hobart will see top of 18 degrees.

A windy day in southern Western Australia is set to keep temperatures about 26 degrees for Perth.

The interaction of the cool airmass with the hot air will likely cause thunderstorms across parts of NSW and the ACT but the cool change late in the day is forecast to bring those temperatures down for the remainder of the weekend.

The relief is forecast to be short lived though, with temperatures due to increase again towards the end of next week.

Olympic Park will be a hotspot in more ways than one, with 100,000 people expected to converge on the Homebush precinct for concerts by the Foo Fighters and 50 Cent tonight.

The conditions are set to put additional pressures on the transport system but Sydney Trains is promising extra services and staff on hand to give out free bottles of water at key stations.

There will also be be extra technical staff on standby should there be any heat-related emergencies and fire trucks on alert for any grass fires on the network.

At Bondi, lifeguards are expecting about 30,000 people to hit the beach in the heat.

"We have extra lifeguards on, we're at full capacity with our staffing and resources," lifeguard Daniel McLaughlin said.

"We're going to see a lot of people with effects to the heat."

NSW Ambulance senior assistant commissioner Clare Beech advises vulnerable people stay indoors.

"Stay indoors if you can during extreme heat, stay hydrated and look after those who are at extreme risk, the very young and the very old," Beech said.