The government of Tonga said the undersea volcanic eruption over the weekend was an "unprecedented disaster", resulting in the deaths of at least three people.
The eruption generated tsunami waves up to 15 metres that hit the west coast of several islands in the Pacific island archipelago, the government said in its first statement since the eruption on 15 January.
International and domestic communications were down as well as internet due to damage from the eruption.
The volcanic eruption was heard as far away as Alaska, more than 9,000 km away.
It produced a huge cloud of smoke 30 kilometres high, which dispersed ashes, gas and acid rain across the Pacific region, which was immediately followed by the onset of a tsunami.
Satellite images showed the extent of the damage, with Copernicus, the European Union's Earth Observation Programme, stating that an estimated 50% of residents near the Tonga capital Nuku'alofa were impacted.
The United Nations said the capital was covered in a two-centimetre layer of volcanic ash and dust.
In aerial images taken by a New Zealand surveillance flight, the coast of an island is lined with trees turned from green to grey due to volcanic ash.
Ash also blanketed fields on the island, images from an Australian Army patrol aircraft showed.
The World Health Organization said had an officer on the ground in Tonga helping to "coordinate the response by channelling information between UN agencies, humanitarian partners and the Tongan government."
But some have said it could have been much worse.
“We did hold grave fears, given the magnitude of what we saw in that unprecedented blast,” Katie Greenwood, the head of delegation in the Pacific for the International Federation of Red Cross and Red Crescent Societies, told the AP.
“Fortunately, in those major population centres we are not seeing the catastrophic effect we thought might happen, and that’s very good news.”