Storms follow temps over 40C as heatwave bakes on

A wave of high temperatures making their way east across Australia could bring storms before an expected easing over the weekend.

Multiple areas around NSW passed 40C on Thursday afternoon, sweltering along with parts of Western and South Australia that have faced severe heatwave conditions this week.

Sea breezes that parts of Sydney rely on for an afternoon cool down were expected to have little effect with temperatures about 10C above average forecast.

The temperature peaked just under 35C at Sydney Airport while further west Canterbury, Homebush, Holsworthy and Richmond all passed 39C.

Penrith hit 40C soon before 3pm.

Parts of Western Sydney including Schofields and Blacktown were also hit by thunderstorms on Thursday afternoon.

Temperatures are forecast to ease on Thursday night in the south of the state, while further north it might not cool down until the weekend.

In the NSW central-west, temperatures had passed 40C at Brewon, Condobolin, Forbes and Girilambone by 1pm.

Further north, Smithville, Noona, Delta, Cobar and Borrona Downs had all hit 40C, while Wilcannia and Bourke reached 42C about 2.30pm.

Severe thunderstorm warnings have been issued for parts of the Hunter region, central west and western Sydney on Thursday afternoon.

There is an elevated fire danger through central NSW, but that is expected to ease on Friday as cooler air moves through.

The severe heatwave conditions had eased over southern NSW but were expected to persist in other areas over the next few days, the Bureau of Meteorology said on Thursday.

Elsewhere, a severe heatwave warning is in place in South Australia's north with maximum temperatures forecast to reach the mid-40s.

It hit 41C at Oodnadatta, 42C at Coober Pedy, and 43C at Marree on Thursday afternoon.

The heatwave's intensity is expected to be reduced in South Australia on Friday.

The hot air is coming from Western Australia after scorching temperatures throughout the week.

Severe heatwave conditions continue over the state's southern interior but have eased in northern districts, the bureau said.

Marble Bar in WA's Pilbara region tipped over 43C just before 2.30pm.

Further south, it did not drop below 30C overnight in Warburton and was back past 43C shortly after noon on Thursday.

Severe heatwave conditions in the ACT have eased after a mid-week peak, however low-intensity heatwave conditions will persist into the weekend, the bureau warned.