Sydney residents are in danger of developing a pack-a-day habit even if they've never smoked.
The spate of bushfires burning across the state means air quality in parts of the city is the equivalent to smoking 34 cigarettes.
Pollution levels are almost twice as bad as that experienced in Delhi, and residents are being warned to stay indoors to limit their exposure to bushfire smoke.
"I can't recall a time where I've seen this before in Sydney and surrounding the region to such an extent," said Centre for Air Pollution, energy and Health researcher Christine Cowie.
"Because this is a relatively new phenomenon, it's really difficult to predict how severe it would be," Cowie is quoted as saying by The Australian.
More bad pollution is predicted on Wednesday, The Sydney Morning Herald reported, after "hazardous" levels were recorded on Tuesday afternoon.
"It's still warm and windy and will remain that way," Rural Fire Service spokesman Ben Shepherd said.
"The main thing we need is rainfall but there's none of that on the horizon," Shepherd told the SMH.
More scorching temperatures on the way
Hot weather will continue for much of Australia with some parts set to scorch in warmer and drier than average conditions.
Rainfall is likely to be below average for large parts of the country's east, according to the NSW Bureau of Meteorology, with potential severe weather risks over the coming months.
Forecasters say this will see Sydney's temperatures sit between the late 20s and early 30s for the rest of this week and start of next.
The hot weather comes as bush fires continue to rage across NSW. A statement from the Bureau of Meteorology said the outlook means the risk of heatwaves has increased.
"It's important the community stays up to date with the latest information and advice from authorities," said head of long-range forecasts Dr Andrew Watkins.
The Bureau of Meteorology has predicted areas of smoke haze in Sydney until at least Sunday.