A heatwave has hit parts of Australia and it's only going to get worse.

It was a scorcher of a day in SA and NSW on Thursday, with COVID-19 testing clinics even having to be closed in Adelaide because of the heat.

The Bureau of Meteorology's heatwave forecasts show there will be small areas of "severe heatwave" around the Cape York Peninsula, the Top End and inland NSW on Friday and Saturday.

There will also be areas of low intensity heatwave over northern NT, Cape York Peninsula and southwest QLD, throughout NSW and parts of northern SA.

The next level above severe in the BOM's assessment is extreme.

The heatwave will continue across the weekend and heading into Monday.

Minimum and maximum temperatures were generally 5 to 10 degrees above average in SA yesterday as the mercury soared to 42.2C in some suburbs.

A maximum of 37C is expected for SA on Saturday.

Victoria also had a hot one, with temperatures hitting more than 35C, the warmest day since January.

Sky News Weather said NSW would reach 38C in Penrith Friday but there could be showers and thunderstorms in the afternoon to cool things off.

"Some of that baking heat will spill over to the coast," they said.

"A cool change will follow but it's not bringing much in the way for wet weather."

Temperatures should cool for the state on Saturday.

Conditions will be dry across most parts of the country.

Meteorologist Ben Noll said the Tasman Sea was 1.6C hotter than normal for this time of year, at 18 to 21C, indicating next month would be warmer than usual heading into summer.

"Now that we've come into November, you can see the ocean temperatures have maintained that warmth," he told Stuff.

"It's fair to say if the warm ocean temperatures persist as we go into summer, chances are we're in for a pretty warm summer here on land as well."

Bureau of Meteorology meteorologist Peter Claassen said Queensland was being with temperatures about 10C above November averages.

The Southern Downs region is nearing crisis point, with Mayor Vic Pennisi saying they will run out of water in 2022 if they get no rainfall.

Brisbane wholesaler Peter Marinos said he bought his fruit and veg from the Darling Downs region but was now shipping in staples from interstate.

"We're getting spinach and rocket all out of Victoria simply because it's just too hot on the paddocks," told 9 News.


Originally published as Heatwave to hit Australia today