Australia's eastern seaboard sweltered Tuesday in unusually warm spring temperatures, with hot winds whipping up some of the riskiest bushfire conditions since the 2019-2020 "Black Summer" catastrophe.

Soaring temperatures in parts of New South Wales have climbed as high as 34 degrees Celsius, more than 10 degrees above the average high for this time of year. 

Children have been sent home from 21 schools in a coastal region 500 kilometres south of Sydney, where firefighters think the most volatile conditions will be felt. 

"Due to stronger than forecast winds along the far South Coast, catastrophic fire danger is expected this afternoon in the region," the New South Wales Rural Fire Service said in a statement on Tuesday. 

"These are the most dangerous conditions for a fire." 

Sydney Harbour was last week shrouded in a smoky haze, as firefighters on the city's fringes lit controlled blazes to deprive bushfires of fuel ahead of a hot and dry summer. 

The spring heatwave sweeping over eastern Australia comes on the back of the country's warmest winter since records began in 1910. 

After several wet years, experts are expecting the coming summer to bring the most intense bushfire season since 2019-2020. 

During that "Black Summer", bushfires raged across Australia's eastern seaboard, razing swathes of forest, killing millions of animals, and blanketing cities in noxious smoke. 

July 2023, marked by heatwaves and fires around the world, was the hottest month ever registered on Earth, according to the European Union's climate observatory Copernicus.