The first humanitarian flights arrived in volcano and tsunami-stricken Tonga Thursday, five days after the dual disaster cut the Pacific kingdom off from the rest of the world.

Tonga has been inaccessible since Saturday, when one of the largest volcanic explosions in decades cloaked the nation in a layer of ash, triggered a Pacific-wide tsunami and severed vital undersea communication cables.

Two large military transport planes from Australia and New Zealand touched down at Tonga's main airport -- only recently cleared of a thick layer of ash after painstaking effort.

"Landed!" said Australia's international development and Pacific minister Zed Seselja, hailing the arrival of a C-17 "carrying much needed humanitarian supplies".

"A second C-17 is now on its way," he added.

Tonga has been virtually cut off from the rest of the world since Saturday's volcanic blast
Tonga has been virtually cut off from the rest of the world since Saturday's volcanic blast NEW ZEALAND DEFENCE FORCE via AFP / Handout

Among the equipment on board was said to be a "skid-steer loader with a sweeper" to help keep the runway clear of ash.

New Zealand confirmed its C-130 Hercules has also landed.

Satellite images show residential homes and buildings in an area of Tonga on December 19, 2021 and the same area on January 18, 2022, after the tsunami
Satellite images show residential homes and buildings in an area of Tonga on December 19, 2021 and the same area on January 18, 2022, after the tsunami Satellite image ©2022 Maxar Technologies via AFP / Handout

"The aircraft is carrying humanitarian aid and disaster relief supplies, including water containers, kits for temporary shelters, generators, hygiene and family kits, and communications equipment," New Zealand foreign minister Nanaia Mahuta said.

More than 80 percent of the archipelago's population of 100,000 have been impacted by the disaster, the United Nations has estimated, and initial assessments indicate an urgent need for drinking water.

The first smattering of images to emerge from Tonga's capital Nuku'alofa show ashen buildings, toppled walls and streets littered with boulders, tree trunks and other debris.

Three people were killed when the Hunga Tonga-Hunga Ha'apai volcano exploded on Saturday, triggering tsunami waves that ripped down homes and caused widespread flooding
Three people were killed when the Hunga Tonga-Hunga Ha'apai volcano exploded on Saturday, triggering tsunami waves that ripped down homes and caused widespread flooding NASA/NOAA via AFP / Handout

Tongans worked for days at the airport trying to clear the runway of ash so that much-needed aid could arrive.

The work was painfully slow, with only a few hundred metres being cleared each day.

Neighbouring countries have relied on surveillance flights and satellite images to assess the scale of the disaster
Neighbouring countries have relied on surveillance flights and satellite images to assess the scale of the disaster Australian Defence Force via AFP / SGT David Gibbs

With the air bridge now open, nations are rushing to get aid in.

Japan has announced it will send two C-130 aircraft, and nations from China to France have indicated they will also provide assistance.

But strict Covid protocols that have kept Tonga virtually virus-free mean the delivery of supplies will be "contactless".

Three people were killed when the Hunga Tonga-Hunga Ha'apai volcano exploded on Saturday, triggering tsunami waves that ripped down homes and caused widespread flooding
Three people were killed when the Hunga Tonga-Hunga Ha'apai volcano exploded on Saturday, triggering tsunami waves that ripped down homes and caused widespread flooding NASA/NOAA via AFP / Handout

New Zealand commander James Gilmour said: "There will be no contact between the New Zealand Defence Force and anyone on the ground."

The crew was only expected to be on the ground for 90 minutes.

Australian military relief ship the HMAS Adelaide is standing by in Brisbane
Australian military relief ship the HMAS Adelaide is standing by in Brisbane Australian Defence Force via AFP / LSIS David Cox

Three people were killed when the Hunga Tonga-Hunga Ha'apai volcano exploded on Saturday, triggering tsunami waves that ripped down homes and caused widespread flooding.

Waves as high as 15 metres (50 feet) were reported to have destroyed almost every home on some outlying islands.

The Tongan government has called the dual eruption-tsunami "an unprecedented disaster" and declared a nearly one-month national emergency.

When the underwater caldera exploded, it fired debris 30 kilometres (19 miles) into the air and deposited ash and acid rain across the kingdom of 170 islands -- poisoning water supplies.

"Water supplies across Tonga have been severely impacted by ashfall and saltwater from the tsunami," said Katie Greenwood of the International Federation of Red Cross and Red Crescent Societies.

There are also fears for the island's food supplies, with a tearful national assembly speaker Fatafehi Fakafanua saying "all agriculture is ruined".

Australia and New Zealand are also sending help by sea, with Royal New Zealand Navy ships HMNZS Wellington and HMNZS Aotearoa expected to arrive in Tongan waters Friday.

They are carrying water supplies and a 70,000-litre-a-day desalination plant, as well as navy hydrographic and dive personnel to survey shipping channels.

Australian military relief ship the HMAS Adelaide is also standing by in Brisbane. It is Canberra's "hope and intent" the ship will depart for the island kingdom Friday, an Australian official said.

HMAS Adelaide will carry "water purification equipment and additional humanitarian supplies", as well as two Chinook heavy-lift helicopters.

The eruption released a pressure wave that traversed the planet, travelling at supersonic speeds of about 1,230 kilometres per hour, New Zealand's National Institute of Water and Atmospheric Research said.

While partial communications were restored Wednesday, mobile phone network provider Digicel said the high number of calls to the island was producing delays.

It is expected to be at least a month before the undersea cable connection is fully restored.