More than 100 flights have been cancelled and there are long delays for travellers in Sydney, as wild winds cut the city’s airport operations to a single runway.

Monday’s delays at Sydney Airport came as wild winds and dangerous surf continued to batter much of Australia’s south-east after days of record-breaking cold temperatures.

An Airservices Australia spokesperson said the decision to move to a single runway in Sydney was due to the “inclement” weather.

“This decision is purely weather-related and is not due to staffing – crosswinds on the parallel runways are up to 30 knots,” the spokesperson said.

The delays, mostly to domestic flights, lasted several hours. The airport returned to full operation by midday.

It came as cold conditions hit the eastern states, and wild winds buffeted 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 of Meteorology is warning of damaging winds affecting wide swathes of South Australia, Tasmania, Victoria, NSW and Queensland.

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

The Bureau of Meteorology issued a severe weather warning on Monday due to a low-pressure system near the South Coast. It was expected to move north-east throughout the day.

“Don’t go anywhere near the water. It will be bad out there today,” meteorologist Dean Narramore said.

Surf is expected to be up to six metres high along parts of the NSW coast on Monday.

Bondi locals said the swell on Monday was among the biggest they’ve seen.

“I have never seen it like that,” one local told Nine’s Today show.

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The weather bureau warned heavy surf could lead to damage and coastal erosion between the Victorian border and Seal Rocks. Conditions were expected 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 BOM 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 life jacket.”

Snow was again falling in Kosciuszko National Park in the NSW Snowy Mountains, with temperatures as low as -4 degrees at 6am on Monday.

Perisher and Thredbo were expecting more snow as temperatures hovered 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 BOM 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 AAP