Cronulla, North Cronulla, Elouera and Wanda beaches have been shut because of swells three to four metres high.
Conditions will be reassessed at 7am tomorrow.
Sutherland beach operations manager Brad Whittaker said the swell had made swimming treacherous for beach-goers.
“It’s a big swell,” he said. “It’s up around four metres.
‘‘It probably peaked this morning and will ease over the next few days.
“We’ve got some light to moderate south-west winds but conditions are not that great for surfing or swimming.
“Cronulla Point is the best option for experienced surfers. There are 4-6-foot-high waves with bigger sets breaking
“The beach tomorrow might look appealing. It is supposed to be a nice sunny day with off-shore winds.
“But the beaches may still be closed depending on the size of the swell.”
WeatherWatch meteorologist Don White said a powerful low pressure system that formed on Wednesday in the central Tasman Sea had triggered the rough conditions.
“It’s quite an intense low,” he said.
“It has moved south-west towards the east of Bass Straight now and has caused a clearing of the weather in Sydney and the big swell.
“The swell will remain around the 3-4-metre-high mark from Sydney down the south coast of NSW.
“It is weakening as it moves south but there will still be a big and potentially dangerous swell again tomorrow.
“Rock fisherman should not go out for 48 hours at least as the swell will remain quite powerful.
‘‘Even as it eases, it will still be dangerous especially for children or adults who are not strong swimmers.”
The big waves have also meant the Ohana Surf Classic Nipper carnival on Saturday is cancelled.
