People in Sydney woke up to a sky shrouded in smoke as wildfires continued to rage across the country.
Strong winds pushed smoke from around 130 fires inland, creating poor air quality in the city.
Officials said the air quality above parts of the harbour city was measured at 10 times the hazardous levels.
They advised people to stay indoors as much as possible as the smoke lingers over coming days.
Australia is prone to bushfires in summer, but fierce blazes have been sparked early by a long drought and soaring temperatures.
Wildfires have so far this month claimed at least four lives, burnt about 2.5million acres of farmland and bush and destroyed more than 300 homes.
“We know that heatwaves cause severe illness, hospital admission and even deaths, and that people are more sensitive to heatwaves early in the season,” Richard Broom, director of environmental health at New South Wales (NSW) Health said.
“The combination of heat and poor air quality adds to the risk.”
The current bushfire crisis has mostly been contained to the east coast and Queensland states, but officials in South Australia warned on Tuesday that forecast near-record temperatures raises risks.
“More than 1,300 firefighters are working on these fires, undertaking backburning operations and strengthening containment lines ahead of forecast hot, dry and windy weather, with seven areas under a total fire ban,” the NSW Rural Fire Service said.
Australia’s Bureau of Meteorology said temperatures in Adelaide, the capital of South Australia, will hit 42C on Wednesday which, coupled with strong winds, will create “catastrophic” fire danger conditions.