FLIGHTS in and out of Sydney have been delayed due to low visibility as a thick layer of fog blankets the city.

The haze is blanketing the city, stretching from the western suburbs to the CBD and Sydney Airport.

Qantas Airways confirmed to news.com.au that it has been impacted by the low-lying fog, with anyone flying today urged to check the flight status website before leaving for the airport.

At least eight Virgin Australia flights have also been affected.

The Bureau of Meterology has warned Sydneysiders to expect traffic chaos and delays across the city this morning.

"Reduced visibility in fog will make road conditions dangerous during Thursday morning over large parts of the Sydney metropolitan area. Motorists are advised to take extreme care," the weather bureau said.

Ferry passengers have also been affected by the fog, with delays and buses replacing ferries between Manly and Circular Quay.

"F1 Manly services are being replaced by buses between Manly and Circular Quay due to heavy fog. Allow extra travel time," said Sydney Ferries Info.

"Make alternative travel arrangements if you normally catch an F2, F3, F4, F5, F6, F7 or F8 service as no ferries are running due to heavy fog.

"No ferries are running due to fog. Make alternative transport arrangements or delay your trip."

If that wasn't bad enough, Sydneysiders had a grumpy start to the morning over a loud fog horn that was sounding across the harbour:

Warmer temperatures have contributed to the fog, with the Harbour City enjoying unusual winter highs of 23 degrees today and tomorrow.