Several days after fuel reduction burns in the Blue Mountains west of Sydney, health authorities have warned residents of now “hazardous” air quality across parts of the city.

The NSW Office of Environment and Heritage reduced the air quality level in the harbour city to “poor” on Wednesday for a second day in a row, with Sydney-siders again waking to hazy conditions and a sharp smell of smoke in the air.

By Friday, the air quality level was deemed “hazardous”, prompting renewed warnings for older people, children and anyone with heart or lung disease to avoid exercising outdoors and to stay inside as much as possible.

Bureau of Meteorology forecaster Chris Ryan said:
 “It’s due to a lack of wind being able to move some of that air out and the wind has been trapped in the basin”.

Conditions are expected to slowly change over the coming days as a tropical front moves over the southern parts of NSW, Mr Ryan said.

Sydney’s west bore the brunt of the fog and smoke haze combination, but some parts of Sydney’s east and northwest also recorded “hazardous” air quality including Richmond, Macquarie Park and Lindfield.

Residual smoke & fog have mixed this morning & settled over Sydney, this will lift over coming hours. There have been no additional burns lit over the past 48 hrs and no further burns today in Sydney. Some smoke is still rising from a #NPWS burn in the Blue Mountains. #NSWRFS

— NSW RFS (@NSWRFS) May 23, 2019

The NSW Rural Fire Service said no additional fires have been lit in the past 48 hours and no further burns are scheduled in Sydney on Friday.

The heavy fog at Windsor affected some train services on the western and north shore lines.

The bureau has forecast clear skies, however, by Friday night for the launch of the 2019 Vivid festival which is set to showcase art, music, light shows and sculptures over the next three weeks.