SYDNEY, April 11 (Xinhua) -- A public health alert has been issued for people in Sydney to take precautions against smoke from planned burns.

Health authorities in the state of New South Wales (NSW) said on Friday that smoke from the burns taking place to the north, west and south of Sydney may affect air quality in the city over the weekend.

The NSW Rural Fire Service and NSW National Parks and Wildlife Service on Thursday began conducting hazard reduction burns in the Blue Mountains National Park, about 75 km west of central Sydney, as well as regions to the north, northwest and south of the city.

Hazard reduction burns are commonly undertaken across Australia outside of bushfire season to reduce fuel loads.

NSW Health on Friday urged people in Sydney, particularly in the western suburbs and Blue Mountains, to monitor air quality levels and follow recommended health advice.

Stephen Conaty, NSW Health's director of Environmental Health, said that smoke particles in the air can irritate the eyes and airways.

"Smoke particles that get into the lung can worsen pre-existing health conditions like angina, asthma, emphysema and diabetes, potentially causing serious illness," he said in a statement.

"In particular, we're urging people to take precautions with infants, young children, and people over 65 years of age who may be more sensitive to the effects of smoke."

As of midday on Friday, the air quality in northwest and southwest Sydney was rated poor.

NSW Health said that people should avoid rigorous outdoor activity, spend more time indoors and wear a facemask outdoors to decrease health risk from smoke.