(CNN) Australians are suffering a brutal post-Christmas heatwave, with temperatures in most parts of the country's southeast up to 14 degrees Celsius (24 degrees Fahrenheit) higher than the average for this time of year.

Some areas of the states of New South Wales, Victoria and South Australia had temperatures above 40 C (104 F) on Thursday -- the fourth day in a row.

Extreme and severe fire warnings have been issued for parts of South Australia Victoria and Western Australia , according to the Australian Bureau of Meteorology.

Pink shading shows where the ECMWF model expects surface temperatures to exceed 40C between Thursday and Sunday. pic.twitter.com/YKt0z9c3LU — Weatherzone (@weatherzone) December 24, 2018

"The cause of the heat is a dome of high pressure settling in over much of the continent over the past few days," CNN meteorologist Gene Norman said.

"In addition to the sweltering temperatures, there is an enhanced fire risk in Victoria, with total fire bans declared for Thursday in the Mallee and Wimmera regions. South Australia has bans in place in 10 areas including the Mount Lofty Ranges and Yorke Peninsula. Western Australia has total fire bans in 13 districts, where temperatures are expected to exceed 45 C in parts."