A Sydney Airport spokesperson said the airport was operating on a single runway due to strong winds.

"This has caused some flight delays and cancellations," the spokesperson said.

"Passengers should speak to their airlines to get the latest information on the status of their flights."

According to the Bureau of Meteorology, Sydney is being hit by 30 to 45 km/hr southwesterly winds.

An Airservices Australia spokesperson said crosswinds on the parallel runways were up to 56km/hr, with stronger gusts possible.

"Airservices will resume parallel runway operations by 11.30am due to easing south-westerly wind conditions," the spokesperson said.

It comes as temperatures plunge in the eastern states and wild winds buffet the coast, bringing dangerous swells and snow inland.

After a relatively mild start to autumn, frosty weather arrived on the weekend courtesy of a low-pressure system off the NSW south coast that's expected to continue this week.

The Bureau is warning of damaging winds affecting wide swathes of South Australia, Tasmania, Victoria, NSW and Queensland.

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In Sydney temperatures dropped to 11 degrees on Monday and winds will average 60 to 70 km/h with peak gusts around 90 km/h over the Illawarra and southern Sydney metropolitan coast.

The Bureau is warning of heavy surf which could lead to damage and coastal erosion between the Victorian border and Seal Rocks, with conditions to ease along the coast south of Batemans Bay on Monday night.

"Significant wave heights of five to six metres are possible, especially on south-facing parts of the coast," the Bureau said.

Spring high tides may compound the impact of waves.

"Beach conditions in these areas could be dangerous and people should stay well away from the surf and surf exposed areas," the Bureau said.

A separate severe weather warning has been issued for damaging surf particularly for Kurnell, Wollongong, Bulli, Port Kembla, Albion Park, Kiama, Jervis Bay and Huskisson.

Marine Rescue NSW Acting Deputy Commissioner Darren Schott is advising boaters to stay off the water in areas where warnings have been issued.

"Boaters planning to cross shallow waters and ocean bars should consider changing or delaying their voyage," he said in a statement.

"Boaters already on the water should carry the appropriate safety equipment and always wear a lifejacket."

Snow is falling in Kosciuszko National Park in the NSW Snowy Mountains with temperatures registering minus four degrees at 6am on Monday.

Perisher and Thredbo are expecting more snow as temperatures hover around freezing.

NSW sheep graziers are warned that cold temperatures and southwesterly winds could affect livestock inland.

"There is a risk of losses of lambs and sheep exposed to these conditions," the Bureau said.

The State Emergency Service is advising people to move cars away from trees, secure loose items around the yard and keep at least eight metres away from fallen power lines.

With Australian Associated Press