Ferries resume as Sydney blanket fog lifts

Most ferry services are operating as normal after fog covered Sydney's CBD but motorists are urged to keep their headlights on as a precaution.

Thursday's fog settled early over Sydney, with several flights out of the city delayed. (AAP)

Most Sydney ferry services have returned to service as a blanket fog covering the city disappears but motorists are urged to be wary on the roads.

Patchy fog settled across the city early on Thursday disrupting some domestic flights at Sydney Airport and ferry services but began to lift by 7.30am, with blue skies appearing.

River ferries to and from Parramatta were still experiencing delays, Transport Management Centre spokesman David Wright told AAP.

Motorists on the Hume Highway and M2, M7, M4 and M1 motorways are also urged to keep their headlights on due to low visibility and wet roads.

"Leave extra space between you and the vehicle in front of you in case of rapid braking," Mr Wright told AAP.

"By doing these things you will be able to get to work a lot quicker".

Passengers are being urged to check with their airlines regarding flight status, due to delays and some cancellations.