Tonga said it has been hit by an "unprecedented disaster" in the government's first official update since a volcanic eruption triggered a tsunami.

In a statement, the prime minister's office confirmed three deaths including two locals and a British national.

Small outer islands suffered particularly bad damage, with an entire village destroyed and many buildings missing, a Tongan diplomat said on Tuesday, raising fears of more deaths and injuries.

"People panic, people run and get injuries. Possibly there will be more deaths and we just pray that is not the case," Tonga's deputy head of mission in Australia, Curtis Tu'ihalangingie, told Reuters.

Tu'ihalangingie said images taken by New Zealand Defence Force (NZDF) reconnaissance flights showed "alarming" scenes of a village destroyed on Mango island and buildings missing on nearby Atata island.

Australia's Minister for the Pacific Zed Seselja said Tongan officials were hoping to evacuate people from the isolated, low-lying Ha'apai islands group and other outer islands where conditions were "very tough, we understand, with many houses being destroyed in the tsunami."

The United Nations had earlier reported a distress signal was detected in Ha'apai, where Mango is located. The Tongan navy reported the area was hit by waves estimated to be 5-10 metres (15-30 feet) high, said the UN Office for the Coordination of Humanitarian Affairs (OCHA).

Atata and Mango are between about 50 and 70 km from the Hunga Tonga-Hunga Ha'apai volcano, which sent tsunami waves across the Pacific Ocean and was heard some 2,300 km (1,430 miles) away in New Zealand when it erupted on Saturday.

Atata has a population of about 100 people and Mango around 50 people.

"It is very alarming to see the wave possibly went through Atata from one end to the other," said Tu'ihalangingie. 

Major airport to open Wednesday at earliest

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 in Saturday's eruption and tsunami but heavy ashfall is preventing full operations, hampering international relief efforts.

The U.N. humanitarian office said Tongan officials had said that clearing the runway would take days, as it was being done manually, with the earliest opening Wednesday.

People on the west coast of the main island of Tongatapu had been evacuated because of "significant damage," OCHA added in an update, while government ministers had broadcast warnings on radio against price gouging amid worries of supply shortages.

Humanitarian aid 

The New Zealand's foreign ministry said two ships, HMNZS Wellington and HMNZS Aotearoa, had departed New Zealand carrying bulk water supplies, survey teams and a helicopter.

Tonga is expected to set out its formal requests for aid today, said Australia's Foreign Minister Marise Payne. 

C-130 flights from Australia could deliver humanitarian assistance including water purification supplies, she said, while the HMAS Adelaide, which would take five days to arrive by sea, was ready to carry engineering and medical personnel and helicopter support for distribution.

"The impact not just of the inundation, but of the extraordinary volume of ash which is covering everything, plus the communications issues, of course, makes this very difficult," she said.

International mobile phone network provider Digicel has set up an interim system on the main island using the University of South Pacific's satellite dish, New Zealand said.

ANZ said the bank's Nuku'alofa branch is open for limited services, although clean water supply and communication were a major challenge for the bank. 

Communication still limited

The archipelago has remained largely cut off from the world since the eruption which cut its main undersea communications cable.

In its update, the Tongan government said the internet was still down, but some local phone services were available and work was under way to restore full communications.

Subcom, a U.S. based private company contracted to repair various subsea cables in the Asia-Pacific, said it was working with Tonga Cable Ltd to repair the cable that runs from Tonga to Fiji.

Samiuela Fonua, the chair of Tonga Cable, said there were two cuts in the undersea cable that would not be fixed until volcanic activity ceased, allowing repair crews access.

"The condition of the site is still pretty messy at the moment," Fonua told the Australian Broadcasting Corp.

The island of Hunga Tonga-Hunga Ha'apai, which sits on the seismically active Pacific Ring of Fire, all but disappeared following the blast, according to satellite images taken about 12 hours later, making it difficult for volcanologists to monitor activity.

Tonga is a kingdom of 176 islands, of which 36 are inhabited, with a population of 104,494 people.