Smoke expected over Sydney again

Hazard reduction burns across NSW are expected to affect Sydney at the weekend, with those vulnerable to respiratory conditions urged to stay indoors.

Sydneysiders with lung conditions should stay indoors as hazard reduction burns continue. (AAP)

Sydneysiders with lung conditions should stay indoors as hazard reduction burns continue around the city.

NSW Health says that burning off will affect residents in areas including the Blue Mountains, Hawkesbury, Hornsby, Central Coast, Hunter Valley, Wollondilly and Queanbeyan.

"Smoke exposure can lead people with lung disease or chronic bronchitis to develop shortness of breath, coughing or wheezing, many days after smoke is inhaled," Deputy Director of Environmental Health Dr Benjamin Scalley said on Friday.