A heatwave has Australia gripped in a seemingly endless summer, with a run of record-breaking temperatures even as autumn officially begins.

The Bureau of Meteorology said the abnormal conditions were affecting almost the entire country in early March, the month which marks the start of autumn.

A lack of rain and cooler winds left the east coast suffering a prolonged stretch of hot and humid weather, it said in a special climate statement released on Friday.

Bureau climatologist Blair Trewin said Tuesday the heat was consistent with the "well-established warming trend in long-term average temperatures" in Australia and globally.

"With overall warming average temperatures you would expect to see more warm extremes and fewer cold extremes -- and that's exactly what we are seeing," Trewin told AFP.

The bureau said the extreme phase of the national heatwave ended around March 9-10, but temperatures remained generally above average.

On the east coast, Sydney continued to sweat, with its Observatory Hill post notching up a record 39 consecutive days of the temperature reaching 26 degrees Celsius (79 degrees Fahrenheit) or above.

The previous record was 19 days set in March 2014.

"Sydney also had a record run of nights above 20 (Celsius)," said Trewin. "They had a run of 25 nights in a row above 20 which was terminated this morning by the narrowest possible margin -- it was 19.9."

Trewin said it was too early to say whether this would be the nation's hottest March, but a number of records had already been smashed with temperatures running 10 degrees above average in some areas.

The report said that over hottest part of the heatwave, maximum temperatures were four degrees Celsius or more above average over most of the continent but 8-12 degrees Celsius above average in much of the southeast.

The report said rainfall was significantly below normal in the country's tropical north, with the northern city of Darwin experiencing its driest January-February since 1965.