An early burst of spring heat is sweeping across Australia this week, with some places experiencing their warmest weather this early in the season for more than a decade.

A hot air mass sitting over northern WA has been transported down to Australia's southern states by a stream of northerly winds ahead of a cold front.

On Tuesday, the heat targeted South Australia and Victoria, where some districts experienced their highest fire danger ratings in five to eight months. In Victoria, it was also the warmest day this early in the season for 11 to 12 years in Horsham (27.5C), Yarrawonga (25.3C), Avalon (25.8C) and Laverton (24.8C).

Tuesday was also the warmest day this early in the season for 19 years at Derby in WA, where the mercury hit 39.8 degrees.

On Wednesday, the warm air will spread across eastern Australia, causing temperatures to climb four to eight degrees above average in part of Queensland and NSW.

Some parts of northern and central NSW are forecast to have their warmest day this early in the season for five years on Wednesday, including Sydney (28C) and Tamworth (27C).

Another pulse of warm air will sweep across the nation's south and southeast during Friday and Saturday, before much cooler air surges over the region, causing a burst of wintry weather at the end of the week.