Air quality in parts of Sydney hit dangerous levels as a blanket of smoke settled across the city on Monday morning due to a number of hazard reduction burns in preparation for the bushfire season.
The NSW Rural Fire Service said the smoke would clear throughout the day and evening, although it warned the smoke might settle in some areas, leading to health alerts for people with lung conditions and asthma.
Data from the NSW Office of Environment showed the worst affected areas were in parts of the inner west, south-west and eastern suburbs where the air quality reached hazardous levels.
The overall air quality for greater Sydney was rated as poor at 10am with the smoke causing havoc for drivers as visibility was ranked low in parts of the south-west, inner west and eastern suburbs.
A number of flights into Sydney Airport were delayed with passengers informed the heavy haze was the source of the problem.
Hazard reduction burning is taking place in a number of areas around Sydney, including the northern beaches, the Hills area, Hawkesbury, Hornsby and Sutherland.
There are further hazard reduction burns around the state including the Blue Mountains, Central Coast, the Illawarra, Southern Highlands and South Coast.
"These are important controlled burns which will reduce the risk to people and properties from bush fires," the RFS said in a statement.
Warm temperatures and low rainfall indicate the state should brace for a "significant" bushfire season, according to research from the Centre for Environmental Risk Management of Bushfires at the University of Wollongong.
NSW Health warns that people with heart and lung conditions, children and older people are more susceptible to the impact of smoke particles in the air.
Dr Ben Scalley, the department's head of environmental health, said smaller particles in the air could travel deep into the lungs and aggravate existing conditions, making symptoms worse.
"It's important that those with pre-existing respiratory conditions like asthma follow their asthma action plan, have plenty of reliever medication handy, and use it as required," he said.
"If symptoms do persist, it's important they seek medical advice."
NSW Health is monitoring hospital presentations and as of Monday afternoon had not seen a spike. It isn't expecting air problems to worsen this week.
The hazard reduction burning will continue throughout the week with the NSW RFS advising operations are scheduled for Bradley's Head at Mosman and from Tuesday to Friday and North Turramurra and the Hawkesbury from Wednesday to Friday.