A number of large fires burning in the Mount Kaputar, Barrington Tops and Wollemi National Parks are producing large plumes of smoke which are drifting across the state.

Easterly winds initially blew smoke from the fire across the Central Tablelands on Saturday with Mudgee, Wellington and Dubbo reporting heavy smoke in the area.

Updated smoking models released on Saturday afternoon however show that the smoke could start moving south, settling across suburbs in the Blue Mountains and Western Sydney.

Rural Fire Services Inspector Ben Shepherd said winds are expected to move smoke further toward western Sydney overnight.

Air quality began dropping on Saturday afternoon and was reported as poor in areas of the Upper Hunter including Muswellbrook.

As the smoke continues to move it could pose a serious health risk to many people including children and elderly people. It could also impact those who suffer from heart and lung conditions.

People suffering from asthma are being advised to reduce their outdoor activities during the heavy smoke period and carry their reliever medication with them at all times.

Residents in the affected area are being warned to keep doors and windows closed and to move outdoor furniture under cover to avoid being burned by embers from the fire.

One of the Hunter fires has burned through almost 7000 hectares and could burn for up to a month as firefighters work to bring it under control. A lack of rainfall forecast for the area will mean it will take some time to full extinguish the blaze.

Emergency services were also kept busy closer to Sydney's CBD and inner eastern suburbs on Saturday afternoon with a grass fire on the headland between Coogee and Gordon's Bay.