Grey clouds of smoke blanket Sydney and Hunter as air quality drops

Bushfires in northern New South Wales have created a blanket of smoke over the greater Sydney and Hunter region today.

A massive 280km perimeter blaze is burning out of control at the Duck Creek Pilliga Forest and has already spread across more than 111,000 hectares.

Warnings were downgraded to a watch and act as emergency services worked overnight to contain the fire while dozens more burned nearby.

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Sydneysiders woke up to clouds of smoke cover today, which authorities confirmed was pushed by northerly winds from the Duck Creek fire.

"Smoke from fires burning in the state's north is currently being experienced across the north-west of NSW, into the Hunter region and down into the Greater Sydney area," NSW Rural Fire Service said in a statement.

"The smoke is expected to clear later this afternoon when forecast southerly winds move through the state."

The air quality has consequently dipped to "poor" in Sydney's northwest today, the NSW Department of Environment has said.

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There are currently 81 fires burning across the state.

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Residents will feel some relief as high temperatures and heatwave conditions have now moved on from most parts of the state.

The Bureau of Meteorology has now forecast a cool change from tomorrow morning.