NSW beaches have been closed for some time on Sunday, January 16

Nippers activities have also been cancelled due to ocean turbulence, unpredictable tides, strong rip currents and hazardous ocean activities.

Any ocean activity is being considered dangerous on Sunday while the warning is current, with Surf Life Saving Illawarra, NSW spokesman Anthony Turner urging people to ditch the fishing rod or surfboard and stay on dry land.

"There's a lot more surging water movements, lot more powerful movements which are possible - people need to heed the warnings," Mr Turner said.

The Bureau of Meteorology's Gabrielle Woodhouse advised people not even to stand near the water as the ocean looked deceiving and had the potential for strong currents to suddenly sweep people out to sea.

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"It is incredibly dangerous, it's a very different sort of wave to what we would normally experience at the beach," Ms Woodhouse said.

It's expected to see "strange currents and rips and waves happening" for periods, then dropping off for some time before suddenly stirring up again.

"It's a situation where you don't want to be near the water's edge or in the water," Ms Woodhouse said.

Tide levels were abnormally fluctuating along the NSW coastline, she said, generated from the tsunami which was triggered by a volcano erupting near Tonga on Saturday afternoon.

"What we're looking at today [Sunday] are more of these quite abnormal waves, affects the NSW coastline - including the Illawarra - it means we're going to have quite unusual and strong tides and currents and rips," the meteorologist said.

An initial land tsunami warning for low-lying coastal areas of Lord Howe Island was downgraded to a marine warning on Sunday morning.

Norfolk Island has also been downgraded to a marine tsunami warning.