Air quality at 'hazardous' levels as smoke haze from fire burns lingers

The Sydney skyline and surrounding suburbs is seen against smoke haze from hazard reduction burns in Sydney yesterday. Photo / AAP

Sydney's air quality worsened today reaching "hazardous" levels as a smoke haze continues to linger over the city, threatening those with respiratory conditions.

Experts are hopeful, however, that conditions will improve tonight.

The Office of Environment and Heritage recorded hazardous conditions - the highest warning available - in Sydney's east, southwest and northwest.

Conditions in the southwest remained hazardous after 3pm NZT, but air quality in the other suburbs improved to "very poor".

The smoke is due to hazard reduction burns carried out by the Rural Fire Service.

Westerly winds continue to push smoke over Sydney as firefighters take advantage of still air and cool conditions to reduce the state's fuel load ahead of an expected dangerous fire season.

The burns will result in more smoke settling over the city due to an "inversion layer" which is locking the air over low lying areas. The Bureau of Meteorology is uncertain when the inversion might break, and whether smaller inversions may follow.

But a spokeswoman told AAP the smoky conditions were easing. "We are expecting stronger winds to pick up ... with the rain that is forecast and we are hopeful that may help to break it," she said.

"Those westerly winds will hopefully blow quite a lot of smoke out to sea and have less of an impact on Sydney residents ... and a smaller inversion certainly won't cause the smoky conditions to the extent that we saw this morning."

The RFS is conducting the burns in anticipation of what is expected to be a very significant fire season. They'll continue as long as conditions allow. NSW Health has warned the particles in smoke can travel deep into peoples' lungs with the elderly, children and people with heart and lung conditions most at risk.

- AAP