A poor air quality alert has been issued for Sydney, where smoke from hazard reduction burns is covering parts of the city.

The Rural Fire Service is carrying out burns in areas including Oatley in south Sydney, the Blue Mountains and Wollongong.

Air quality has already dropped from ‘good’ to ‘fair’ in areas including Parramatta, Penrith, Richmond, Bargo, Oakdale, Camden, Liverpool and Campbelltown west.

Air quality is expected to worsen over the course of the day and drop to ‘poor’, which means those who may suffer from shortness of breath or coughing should avoid outdoor physical activity.