All homes on one of Tonga's islands destroyed, 3 people dead

All the homes on one of Tonga's small outer islands have been destroyed by a massive volcanic eruption and tsunami, with three people so far confirmed dead, the government said on Tuesday in its first update since the disaster struck.

With communications badly hampered by the severing of an undersea cable, information on the scale of the devastation after Saturday's eruption had mostly come from reconnaissance aircraft.

But the office of Prime Minister Siaosi Sovaleni said in a statement that every home on Mango island, where around 50 people live, had been destroyed, only two houses remained on Fonoifua, and Namuka island had suffered extensive damage.

Tonga's deputy head of mission in Australia, Curtis Tu'ihalangingie, earlier said pictures taken by the New Zealand Defence Force (NZDF) showed "alarming" scenes of a village destroyed on Mango and buildings missing on Atata island, which is closer to the volcano.

"People panic, people run and get injuries. Possibly there will be more deaths and we just pray that is not the case," Tu'ihalangingie told Reuters.

Sovaleni's office said a 65-year-old woman on Mango island and a 49-year-old man on Nomuka island had been killed, in addition to the British national whose body was found on Monday. A number of injuries were also reported.

Tsunami waves reaching up to 15 metres hit the Ha'apia island group, where Mango is located, and the west coast of Tonga's main island, Tongatapu, the prime minister's office said. Residents were being moved to evacuation centres as 56 houses were destroyed or seriously damaged on that coast.

Atata and Mango are between about 50 and 70 kilometres from the Hunga Tonga-Hunga Ha'apai, which sent tsunami waves across the Pacific Ocean when it erupted with a blast heard 2,300 kilometres away in New Zealand.

Satellite images from Sunday show the caldera of Hunga Tonga-Hunga Ha'apai has collapsed and the island has lost a substantial percentage of its initial surface area, said the UN Office for the Co-ordination of Humanitarian Affairs (OCHA).

A rescue operation began on Sunday for Atata island, which has a population of about 100 people, with an evacuation underway.

"Challenges to sea and air transportation remain due to damage sustained by the wharves and the ash that is covering the runways," the prime minister's office said.

A thick layer of ash blankets the islands, the aerial images provided to Tonga by New Zealand and Australia showed.

The archipelago's main airport, Fua'amotu International Airport, was not damaged but the ash was having to be manually cleared from the runway, with the earliest opening being on Wednesday, the OCHA said.

As well as the damage locally, scientists say the eruption could have a long-lasting impact on coral reefs, coastlines and fisheries in the wider region, as well as causing acid rain.