Thick fog has blanketed Sydney, disrupting flights, ferries and motorists across the city.
Several flights were grounded at Sydney Airport and some incoming services diverted to other cities, although services returned to normal mid-morning.
Sydney Ferries also resumed operations after suspending all services for several hours.
Meanwhile poor visibility also impacted on several highways, including the M1 and M4, with drivers urged to slow down.
A high-pressure system off the coast, coupled with moisture with light winds and clear skies on Friday night reduced visibility.
Neil Fraser from the Bureau of Meteorology said fog like this occurred about three times each year.
"Looks like it's fairly widespread," he said.
"At the moment the airport's got a decent north westerly blowing, about 13 kms an hour.
"It forms elsewhere and then drifts across to the airport."
The Transport Management Centre said the M1 Pacific Motorway was affected between Hawkesbury River Bridge and Calga.
The M4 was also affected in both directions around Prospect and Eastern Creek.
Drivers were urged to take extra care on the Hume Motorway and Hume Highway between Campbelltown and Liverpool in both directions.