With the mercury tipped to hit 44 on Saturday and 45 on Sunday across parts of NSW, the outback town of Ivanhoe will be one of the state's hottest.
However, Sydney's outer west isn't far behind, with Penrith likely to reach 40C three days in a row from Saturday.
Coastal areas will experience some relief with the sea breeze expected to keep temperatures down, Bureau of Meteorology meteorologist Grace Legge said.
"This intense heat and dry weather conditions have led to fire weather warnings," she said.
A total fire ban has been declared by the RFS for central NSW, the Hunter region, north western NSW and the northern and southern slopes
Residents across the state have been urged to prepare their homes in case of a bushfire and remain vigilant as the temperatures heat up.
NSW Health says residents in the city's greater west need to avoid strenuous outdoor activity and stay hydrated with poor air quality forecast.
"Ozone levels are higher outdoors than indoors, so limiting time outside during the heat of the day and especially in the evening would help people to keep cool and limit their exposure to ozone pollution," NSW Health Medical Advisor Dr Adi Vyas said in a statement.
"As ozone can irritate the lungs, people with asthma need to follow their Asthma Action Plan and take their relieving medication where necessary."
Meanwhile, the Australian Veterinary Association has warned farmers to take measures to protect their livestock in the extreme heat.
AVA President Dr Paula Parker said livestock and horse owners should ensure water supply is high, hose animals down and make dietary changes to account for lost electrolytes.
