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Sydney is covered in a wall of white this morning as thick fog engulfs the city, obscuring iconic landmarks and delaying flights.

Footage filmed from a helicopter flying over the CBD shows fog completely obscuring the area, with only the tops of the tallest buildings visible.

At ground level, traffic can hardly be seen, impacting travel times due to the low visibility.

Flights to and from Sydney Airport are experiencing delays of up to two hours, which are causing havoc to some passenger's travelling during this NSW Queens Birthday long weekend.

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A blanket of thick fog covers the Sydney CBD this morning (pictured in Barangaroo), obscuring all but the tallest buildings 

The top of the city's Sydney Tower is pictured this morning, almost completely obscured by the thick fog 

Weatherzone meteorologist, Craig McIntosh, said the fog has been caused by the large amount of moisture in the air following the rain in the city over the last few days.

'The recent rain has added humidity to the atmosphere, and as the air cools overnight it allows fog to form,' he said.

Mr McIntosh added that the fog formed in the east of the city and then drifted toward the Eastern Suburbs, pushed along by light winds.

Exactly how long the fog will remain is not clear.

'The fog is expected to linger in the most sheltered valleys and around rivers well into the morning,' Weatherzone meteorologist Brett Dutschke told the ABC.

The Anzac Bridge pictured from Pyrmont covered in the thick fog this morning 

The unexpected heavy blanket of fog caused people to take to social media, with comments ranging from admiration to alarm

He added that this was ' because we're not getting the burning off effect of the sunshine because we've got still a fair bit of high cloud about.'  

The unexpected heavy blanket of fog caused people to take to social media, with comments ranging from admiration to alarm.

'Beautiful never seen anything like it,' wrote one Facebook user.  Another commented 'visibility zero.'

'Where's Sydney gone?' wrote one, while others focused on the fog and concerns about flying and flights to and from the city.

'So happy I'm not flying in that! posted one, while another commented: 'Sydney let's hope flights aren't delayed.' 

The heavy blanket of fog (pictured) descended over Sydney this morning, completely covering the Harbour Bridge, but should be mostly cleared by midday, according to meteorologists from Weatherzone, and the Bureau of Meteorology 

Meteorologists expect the fog (pictured) to be largely gone by midday, but it may return tomorrow morning 

The tops of building in Sydney's Barangaroo district (pictured) covered by heavy fog this morning 

ABC reported that visibility at the airport has dropped below 500 metres at times, which is low enough to cause flight delays and even some flight diversions. 

Some passengers on social media were noting flight delays of two hours.

A spokesperson for Sydney Airport told Daily Mail Australia that at the present time, the fog was causing delays, mostly to arrivals, of up to 30 minutes at the International Airport.

Delays to flights at the domestic airport were longer, averaging 90 minutes to two hours.

Passengers concerned about their flights should contact their airlines for further information, the spokesperson said. 

Meteorologist, Katarina Kovacevic, from the Bureau of Meteorology, said although the fog will probably dissipate today, there is still a risk of fog again tomorrow throughout the Sydney basin.

And for those in the Western Suburbs of the city, the fog might still be around during the NSW public holiday on Queens Birthday Monday, she said.