A mix of smoke and fog is reducing visibility and air quality in eastern NSW today.

Persistent northerly winds were transporting smoke along the coast and adjacent inland of NSW on Thursday morning. Most of this smoke was coming out of fires on the state's northern and mid-north coasts, before being carried hundreds of kilometres to the south.

The airborne particles from this smoke helped produce areas of thick fog along the state's central and southern coasts. The combination of smoke and fog reduced visibility to 100-200 metres at Taree and Moruya and less than 1500 metres in parts of Sydney on Thursday morning.

Image: Visible satellite image showing smoke and fog over eastern NSW at 9am EDT on Thursday.

The average air quality across Sydney, the Illawarra and Lower Hunter during the 24 hours to 8am on Thursday was Very Poor to Hazardous based on airborne particles associated with the smoke. These are the two highest categories in a six-tiered scale.

Smoke will linger over eastern NSW throughout Thursday as northerly winds persist along the coast. Stronger winds on Friday should help disperse some of the smoke, but will also raise fire danger ratings in some parts of the state.

Visit https://www.rfs.nsw.gov.au/ for the latest information on fires across NSW.