Tsunami alert keeps NSW beaches closed

Waves more than one metre high have been recorded on Australia's east coast, after a massive underwater volcano erupted near Tonga in the Pacific.

While several tsunami marine alerts have now been cancelled on Australia's east coast the Bureau of Meteorology said it had detected large waves and the NSW SES said beaches across the state would stay closed.

Bureau of Meteorology Meteorologist Sarah Scully said a wave of 1.27m was recorded on Norfolk Island.

New South Wales coast are closed due to a tsunami warning after an undersea volcano erupted off Tonga.

The Gold Coast saw a wave 87cm high, and Twofold Bay near Eden in NSW had a 77cm wave.

"So an enormous amount of energy was released by the volcanic eruption, and that was trapped by the oceans. So it travelled thousands of kilometres to impact not just the East Coast of Australia but many nations throughout the Pacific Ocean," she said.

Lifesavers keep a watch on the ocean at Bondi Beach in Sydney, due to a tsunami warning.

Beaches were closed this morning from the Sunshine Coast to the New South Wales border, after a violent eruption, which was seen from space and heard as far away as Alaska over 9000km away.

Warnings in Tasmania, Victoria and Queensland and Macquarie Island are no longer in effect, a Bureau of Meteorology spokesperson said.

Bondi Beach was open this morning and then closed again due to a tsunami warning after a South Pacific undersea volcano erupted off Tonga.

However, warnings remain in effect for New South Wales, Lord Howe Island and Norfolk Island.

The BoM said there is the possibility of dangerous rips, strong ocean currents and some localised overflow onto the immediate foreshore.

"While evacuations are not necessary for marine threat areas, people in these areas are advised to get out of the water and move away from the immediate water's edge," the BoM said.

A satellite image taken by Himawari-8, a Japanese weather satellite, shows the undersea volcano eruption near Tonga.

NSW SES Assistant Commissioner, Sean Kearns, said the public must stay clear of the water.

"The surf conditions will likely remain hazardous well into tomorrow," Mr Kearns said.

"There is also a chance we could experience severe weather this afternoon, which could only add further dangers," he said.

Last night Bondi Beach was evacuated around 10:30pm, with police and SES calling everyone off the beach and away from the ocean.

This morning Bondi Beach was briefly open, with regular surf safety flags put out for swimmers, but the flags were soon taken down with everyone discouraged from entering the sea.

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Nippers and an Ironman series event set to take place at the Sydney beach today were cancelled.

"Can I just ask everybody to please follow the instructions of the SES, of surf lifesaving," Premier Dominic Perrottet said.

"Beaches are closed, please do not swim."

The Bureau of Meteorology is monitoring potential threats, and State Emergency Services (SES) Commissioner Carlene York said she expected beaches to be closed until 4pm (AEST).

She anticipated a 1.1-metre tsunami wave recorded at Lord Howe Island would eventually hit NSW.

Lord Howe Island also experienced unusual currents and waves, according to reports.

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Tsunami advisories were issued for New Zealand, Hawaii, Alaska and the US Pacific coast.

In the US, a tsunami surge swamped a car park in Santa Cruz, California.

All the water receded before it flooded again.

A tsunami surge inundates the parking lot at the top of the Upper Harbor in Santa Cruz, California.

On Tonga, home to about 105,000 people, video posted to social media showed large waves washing ashore in coastal areas, swirling around homes, a church and other buildings.

Tonga's King Tupou VI was evacuated from the Royal Palace, with a convoy of police and troops rushing the monarch to a villa at Mata Ki Eua, according to reports.

Satellite images showed a huge eruption, with a plume of ash, steam and gas rising like a mushroom above the blue Pacific waters.

Ash was falling from the sky in the capital of Nuku'alofa on Saturday evening and phone connections were down, Radio New Zealand reported.

In this satellite photo taken by Planet Labs PBC, an island created by the underwater Hunga Tonga Hunga Ha'apai volcano is seen smoking on January 7. An undersea volcano erupted near Tonga yesterday, sending large tsunami waves crashing across the shore and people rushing to higher ground.

A spokesperson for the United Nations offices in the Pacific "are closely monitoring the situation and are on standby to provide support if requested".

"The Secretary-General is deeply concerned by the reports of a tsunami and ash affecting Tonga, as well as of resulting tsunami warnings that have been issued in other countries," the spokesperson said.

"The Secretary-General is grateful to countries that have already offered their support."

The explosion of the Hunga Tonga Hunga Ha'apai volcano was the latest in a series of dramatic eruptions.

Earth imaging company Planet Labs PBC had watched the island in recent days after a new volcanic vent there began erupting in late December.

Satellite images captured by the company show how drastically the volcano had shaped the area, creating a growing island off Tonga.