A large blaze brought an emergency warning to Adelaide in South Australia on Monday, while neighbouring Victoria faced its worst fire risk in a year.
Victoria's capital Melbourne reached 30C by 07.30 local time (20.30 Sunday GMYT) ahead of an expected 40C maximum.
Temperatures in Sydney were also forecast to exceed 30C for a third day.
Health officials have urged people to stay inside and to avoid physical activity, and for those near bushfires to avoid inhaling smoke.
The blaze in the Adelaide Hills strengthened on Monday on the back of the hot and gusty conditions.
It has so far burnt over 2,500 hectares and is believed to have claimed several houses but has not caused injuries, said South Australia's Country Fire Service.
Smoke has also settled over Adelaide, obscuring parts of the city skyline and prompting some residents to wear face masks.
Photo caption: A bushfire burning in the Adelaide Hills