Why does Sydney smell like smoke this morning?

An air quality warning has been issued for Western Sydney as firefighters complete hazard mitigation burns.

Two hazard mitigation burns are underway in Kur-ring-gai Chase National Park and Katoomba.

Air quality warnings are currently in force for Richmond and Penrith, with haze spreading across the city and its residents.

Many residents had a sleepless night due to the strong smoke smell.

Residents in affected areas are advised to take precautions by closing windows and doors until air quality improves.

These burns are one of many risk mitigation operations undertaken each year by NSW National Parks and Wildlife Service, many with assistance from the NSW Rural Fire Service and Fire and Rescue NSW.