Australians are in for a scorcher on Wednesday with a heatwave sweeping across the country, bringing above 40 degree temperatures to some parts.

In what will be the hottest day of summer so far, temperatures on Wednesday are tipped to reach more than 40 in northwest Victoria - including a sizzling top of 43 for Mildura, the Bureau of Meteorology says.

The rest of the state can expect temperatures into the high 30s, while Melbourne could reach 37.

Sydney's heatwave will set in a bit later with a high of 35 expected on Thursday and Canberra will feel the warmth with five days above 30 degrees.

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Expect to see packed public swimming pools around Melbourne in coming days. Source: Getty

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Beaches around the east coast will be swamped by those trying to beat the heat. Source: Getty

In Victoria, there are fire bans in place for the Mallee and Wimmera - the first of the state's summer season.

"Northerly winds are expected to become quite gusty over western and central parts of the state and that will drive fire dangers into severe (category) across the Mallee and Wimmera," Senior Meteorologist Rod Dickson said.

"But it will be a short-lived heat event for Victoria with a cool change moving into the west of the state during the late afternoon."

The cool relief will hit Melbourne on Wednesday after 9pm and should drop temperatures by about 10 degrees.

The mercury is set to soar above 30 across all capital cities, even Hobart will reach 31 on Wednesday.

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