A dense blanket of fog surrounding Sydney has delayed flights and caused ferry services to be cancelled.

All Sydney Ferries services that use Sydney Harbour including the Manly Ferry have been suspended due to Saturday’s heavy fog.

There is no forecast as to when services will resume, the Transport Management Centre said.

Passengers are advised to delay their journey, use alternative public transport and allow additional travel time.

Outgoing air travellers experienced short delays on Saturday morning thanks to the morning fog.

“There are still flights coming in, but obviously for safety reasons everything is slowed down,” a spokeswoman from Airservices Australia said.

“Conditions will start improving from what they were earlier.”

Sydney Airport’s overnight flight curfew meant only some flights after 6am were affected.

Meanwhile, the NSW Transport Management Centre has warned motorists to take caution, particularly on major highways.

The Bureau of Meteorology expects northwesterly winds of 15 to 20 km/h in the early afternoon and sunny conditions.

The bureau warns deceptively powerful surf conditions during the day are expected to be hazardous for rock fishing and swimming.