Forecast extreme heat and strong winds have led to total fire bans across about one third of New South Wales, the NSW Rural Fire Service (RFS) says.

There are total fire bans in eight areas that stretch from the Victorian border to the lower central western plains.

The RFS said the fire danger rating was severe in seven of those areas.

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RFS spokesman Paul Best said the eighth area on the state’s far south coast had a very high fire danger rating.

“Very high is lower than severe, but bear in mind, major fires can still occur at the lower end of the fire danger rating,” he said.

“We saw very early in the fire season a fire threaten homes in the Blue Mountains burning at low to moderate, so, although it is lower than severe, it certainly is still a bad fire day.”

Mr Best said the expected hot weather and strong winds created dangerous fire conditions.

“[We’re expecting] strong winds today from the north, north-west and that will reduce the humidity, so that, coupled with those warm temperatures, [has] driven the fire danger ratings up into that very high and severe rating across many parts of the state,” he said.

Total fire bans are in place for the Lower Central West Plains, Northern, Southern and Eastern Riverina, Southern Slopes, Southern Ranges, the Illawarra/Shoalhaven and the Far South Coast districts.

There are reports a fire in the Kosciusko National Park in the Snowy Mountains has breached containment lines.

RFS Commissioner Shane Fitzsimmons said crews would tackle the fire from the air.

“We’re about to do some more water bombing to try to halt the forward spread of that fire with the large air tanker operating out of Canberra,” he said.

“As a contingency we’re talking with campers in the likes of the Tom Groggin and Geehi camping grounds.”

The RFS is advising residents in Sydney’s north and the Central Coast that smoke in the area is coming from fires in the Hawkesbury and Hunter regions.

Cool change expected about midnight

The heat in New South Wales has been concentrated in the south-west, but will spread up and across the state, with hot air pushed from Victoria and South Australia.

Bureau of Meteorology forecaster Christopher Webb said there had been several days of extreme heat in parts of the state.

“The combination of the trough crossing and the north-westerly winds strengthening and further hot temperatures [bring] those fire dangers up into the severe range,” he said.

“A strengthening of the north-westerly wind, which is going to be hot, and dry … that’s bad for fire danger.”

Mr Webb said a cooler southerly change was expected to come up the coast from about midnight on Sunday.

The RFS said no fires may be lit in the open and all fire permits had been suspended.

In Victoria eight properties have been lost in a large out of control bushfire near Ballarat, as authorities warn of another day of extreme temperatures across the state.

South Australia sweltered through record heat on Saturday, with Port Augusta reaching 47.2 degrees Celsius.