Sydney was blanketed in a smoky haze on Tuesday morning, after weekend hazard reduction burns left parts of the city with air quality so poor it was more than twice the hazardous level, and more than five times as bad as the air quality in Beijing.

Smoke from weekend hazard reductions, including a large state forest burn at Colo Heights on the weekend, was still covering Sydney on Tuesday, and NSW Rural Fire Service spokesman Ben Shepherd said it was not expected to clear until Wednesday.

Air quality in parts of Sydney was more than two times the hazardous level. Credit:Janie Barrett

"Over last 24 hours there haven't been any new ignitions, but some of those have continued to burn," he said.

"What we've seen across Sydney is relatively light winds, so a lot of this smoke has basically hung around in the basin, and moved around.