The extent of damage following a huge volcanic eruption and subsequent tsunami remains to be revealed at its epicentre near Tonga, but its impact was felt right around the Pacific and, indeed, around the other side of the world.

When the Hunga Tonga Hunga Ha'apai volcano erupted on Saturday, it caused a plume of ash, steam and gas to rise like a mushroom above the blue Pacific waters.

It lead to tsunami warnings and evacuation orders in several countries, and caused huge waves on several South Pacific islands.

In Peru, two people drowned off a beach after unusually high waves hit coastal areas.

A sonic boom could be heard as far away as Alaska and tsunami waves battered boats in Japan, New Zealand and California, but did not appear to cause any widespread damage.

There were reports of floods in parts of Fiji, Chile and Ecuador.

In Tonga, it sent tsunami waves crashing across the shore and people rushing to higher ground.

Ash cloud goes stratospheric

Dr Heather Handley — a volcanologist and Adjunct Associate Professor at Monash University — said the effects of the eruption were felt all around the world.

"The ash and gas plume from Saturday's eruption reached the stratosphere," she said.

"Present estimates indicate that the plume reached 30 kilometres [above the Earth], making it a very powerful eruption."

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It was unclear if further eruptions would happen, she said.

"But volcanic activity is likely to continue over the coming days," she said.

The eruption was so powerful, it was detected at a Scottish weather station.

Professor Hannah Power, who is a coastal and marine scientist at the University of Newcastle, described how far the impact travelled.

"The sea level gauge at Nuku'alofa, Tonga, recorded a tsunami wave of 1.19 metres before it stopped reporting," she said.

"Waves of [more than] a metre were also observed in Vanuatu and Norfolk Island, Australia, and as far afield as Chile.

"Waves of over 50 centimetres were measured in several locations in New South Wales, Queensland, Fiji, the Cook Islands, New Caledonia, and New Zealand.

"Across the Pacific, tsunami waves were observed along both the North and South American coastlines and in Japan."

Professor Power said small but measurable waves were still being detected in Australia as a result of the tsunami.

Concerns for people on islands near eruption

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New Zealand Prime Minister Jacinda Ardern said Tonga's capital, Nuku'alofa, was covered in a thick film of volcanic dust, contaminating water supplies and making fresh water a vital need.

However, so far, it seems none of the country's 105,000 inhabitants were killed, although concerns remain for the fate of people on some of the smaller islands nearer the volcano, which lies 65km north of Tonga.

On Monday, the deputy head of mission at the Tongan High Commission in Australia, Curtis Tuihalangingie, said there had, so far, been minimal damage reported.

Mr Tuihalangingie said he had spoken with family and friends before communication was cut, and they described the eruption as "unbelievable".

"They were not able to explain to us the noise and the sound and what happened at the time," he said.

People on Tonga described their country as looking like a moonscape as they began the task of cleaning up from the tsunami waves and ash fall caused by the eruption.

On Monday, Australia and New Zealand sent surveillance flights to further assess the extent of the damage.

A towering ash cloud had prevented either nation's military from launching any flights earlier to the Pacific island nation.

Australia has also announced an initial humanitarian aid package of $1million, while New Zealand has offered $NZ500,000 ($472,000), with a promise of more when further help is needed.

Ports closed, coastal homes flooded

More than 20 Peruvian ports were temporarily closed as a precautionary measure amid warnings that the volcano was causing abnormally high waves, Peru's National Institute of Civil Defence said.

Peruvian police said two bodies were found by officers, and the area where they were located has since been declared unsuitable for bathers.

TV images showed several homes and businesses flooded by seawater in coastal areas in northern and central Peru.

The Peruvian Navy had reported that a tsunami alert was ruled out.

Japan issues first tsunami warning in years

In Japan, about 230,000 people were advised to evacuate on Sunday as waves of more than a metre hit coastal areas.

The country's meteorological agency issued tsunami warnings in the early hours on Sunday.

Public broadcaster NHK said no damage nor casualties had been reported, interrupting its regular programming to report on the tsunami advisory spanning the entire eastern coast of the Japanese archipelago.

In a briefing, a Japan Meteorological Agency official urged people not to go near the sea until the tsunami advisory and more serious tsunami warnings had been lifted.

The alert is still in place only in Japan's prefecture of Iwate, the area devastated by the 2011 massive quake and tsunami, while other prefectures facing the Pacific, from Hokkaido in the north to Kagoshima and its remote islands, have been placed under tsunami advisories.

The warnings were the first in more than five years.

The ash cloud also led to a flight from Japan to New Caledonia being diverted to Brisbane overnight on Sunday.

People told to stay away from US coast

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

Residents were advised to move away from the coastline to higher ground and to pay attention to instructions from their local emergency management officials.

"We don't issue an advisory for this length of coastline as we've done — I'm not sure when the last time was — but it really isn't an everyday experience," the tsunami warning coordinator for the National Tsunami Warning Center in Palmer, Alaska, Dave Snider, said.

The US Geological Survey estimated the eruption caused the equivalent of a magnitude-5.8 earthquake.

ABC/Wires