The Joint Australian Tsunami Warning Centre issued a tsunami warning for the entire NSW coastline Saturday night, which continued through Sunday following an undersea volcanic eruption off Tonga.

Director of the Far South Coast Surf Life Saving branch Cheryl McCarthy said individuals should not be fooled by seemingly calm waters and instead remain vigilant and mindful of unpredictable water movements.

"We're not looking at big waves coming out of nowhere, but some really strong rips that are coming through in places we'd not normally see them," Ms McCarthy said.

"Just because there's no waves or they aren't very big in a particular area, doesn't necessarily mean it's safe," she added.

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Ms McCarthy said Surf Life Saving NSW members have noticed some very strong currents in the waters and highly recommend, if people swim at all, they do so at patrolled beaches and in-between the flags.

"Even though some of the beaches look relatively calm, there's a lot of water moving around," Ms McCarthy said.

"It's really unpredictable at the moment so patrolled beaches are your best bets," she said.

To stay informed on where the nearest patrolled beach is, people can download the Beachsafe app onto their mobile phones.

Ms McCarthy said for those who aren't confident swimmers or are bringing children to the beach, make sure you're not getting in the water.

"Even if you have the kids just paddling on the very edge of the water, that can still be dangerous," she said.

Ms McCarthy explained that although the kids might just be playing on the edge of the water, the water movements were dangerous enough to cause sudden accidents.

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"If you're not right there with them, they can get taken off their feet very quickly. So if you can't be at a patrolled beach, then I would say yeah, enjoy your beach time from on the sand."

Ms McCarthy said lifesaver volunteers noticed a lot of people heading to the beaches on Sunday, following the tsunami alert released Saturday night.

"We noticed a lot of people coming down to the beaches to have a look, but for the most part, people were staying out of the water, which was really great to see," she said.

Ms McCarthy said to the disappointment of some, there hadn't been much swell to see at the beaches on the Far South Coast.

"A lot of people were expecting to see big waves come through but it really just came in a number of surges where the water came surging out and then back in over a period of 20 minutes at a time," Ms McCarthy said.

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Ms McCarthy said the surf lifesaving volunteers were still on duty, patrolling beaches and ensuring people's safety, despite the beaches being closed on Sunday.

"Our teams were fully manned, we were still out on the water and on inflatable rescue boats to help ensure people were safe," she said.

Ms McCarthy said the lifesavers also had people come up to them at the beaches to have a chat.

"Lots of people came down yesterday to chat with our team members. They were curious and wanted to check what's going on," she said.

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