Sydney's air quality worsened overnight as a smoke haze continues to linger over the city.
Sydney's air quality is improving after it reached "hazardous" levels as a smoke haze lingered over the city for two days threatening the health of infants, the elderly and people with respiratory conditions.
The Office of Environment and Heritage recorded hazardous conditions - the highest warning available - in Sydney's east, southwest and northwest on Tuesday morning.
The smoke was due to hazard reduction burns carried out by the Rural Fire Service. It lingered longer than anticipated because of an "inversion layer" in the atmosphere.
Winds pushed smoke over Sydney as firefighters took advantage of still air and cool conditions to reduce the state's fuel load ahead of an expected dangerous fire season.
NSW Health warned the particles in the smoke could travel deep into peoples' lungs with the elderly, children and people with heart and lung conditions most at risk.
Air quality in the southwest remained hazardous until mid-afternoon on Tuesday and then started to improve.
By evening, the southwest and northwest regions were rated "very poor" while the city's east was slightly better off with "poor" air quality.
Bureau of Meteorology senior forecaster Jake Phillips says winds will sweep through the city on Wednesday clearing most of the smoke.
"We'll see a lot more wind tomorrow mixing things up and dispersing the smoke - it should be a lot better," he told AAP.
Air quality forecasters are tipping "fair" conditions across the city.
The winds will be northwesterly shifting westerly through the day and will become gusty by late morning and into the afternoon, averaging 40 to 50 km/h, Mr Phillips says.
However, hazard reduction burns near the city will continue with the RFS scheduling burns in the Hawkesbury region's Scheyville National Park and also the Ku-ring-gai bushland north of Sydney this week.