Frightened Tongans fled to higher ground Saturday after a massive volcanic eruption -- heard in neighbouring countries -- triggered tsunami warnings across the South Pacific.

"A 1.2 metre tsunami wave has been observed at Nuku'alofa," Australia's Bureau of Meteorology tweeted.

The latest eruption of the Hunga Tonga-Hunga Ha'apai volcano came just a few hours after a separate Friday tsunami warning was lifted due to the eruption.

Mere Taufa said she was in her house getting ready for dinner when the volcano erupted.

"It was massive, the ground shook, our house was shaking. It came in waves. My younger brother thought bombs were exploding nearby," Taufa told the Stuff news website.

She said water filled their home minutes later and she saw the wall of a neighbouring house collapse.

"We just knew straight away it was a tsunami. Just water gushing into our home.

"You could just hear screams everywhere, people screaming for safety, for everyone to get to higher ground."

Tonga's King Tupou VI was reported to have been evacuated from the Royal Palace in Nuku'alofa and taken by a police convoy to a villa well away from the coastline.

The initial eruption lasted at least eight minutes and sent plumes of gas, ash and smoke several kilometres into the air.

Residents in coastal areas were urged to head for higher ground.

The eruption was so intense it was heard as "loud thunder sounds" in Fiji more than 800 kilometres (500 miles) away, officials in Suva said.

Fijian officials warned residents to cover water collection tanks in case of acidic rain fall.

Victorina Kioa of the Tonga Public Service Commission said Friday that people should "keep away from areas of warning which are low-lying coastal areas, reefs and beaches".

The head of Tonga Geological Services Taaniela Kula urged people to stay indoors, wear a mask if they were outside and cover rainwater reservoirs and rainwater harvesting systems.

The Pacific Tsunami Warning Centre issued a "tsunami advisory" for American Samoa, saying there was a threat of "sea level fluctuations and strong ocean currents that could be a hazard along beaches".

Similar warnings were issued by authorities in New Zealand, Fiji, Vanuatu and Australia -- where authorities said a swathe of coastline including Sydney could be hit by tsunami waves.

People in surrounding New South Wales state were "advised to get out of the water and move away from the immediate water's edge".

The Hunga Tonga-Hunga Ha'apai volcano sits on an uninhabited island about 65 kilometres (40 miles) north of the Tongan capital Nuku'alofa.