* From Italy to Invercargill - why the Tongan explosion was heard around the world
* First images from Tonga show scenes of devastation
* Why the volcanic eruption in Tonga was so violent, and what to expect next
A Royal NZ Air Force Orion has left for Tonga to assess the damage caused by the mammoth volcanic eruption over the weekend - and determine exactly what help the island kingdom needs.
The NZ Defence Force announced early this morning that an Orion aircraft had left for Tonga, from Auckland, and would make an initial assessment of the area and low-lying islands on arrival.
"We will provide more information once the situation and ways we can help become clearer. Our thoughts are with those who have been affected at this time."
The violent South Pacific volcanic explosion, heard from Italy to Invercargill, has left Tonga covered in ash and looking like a "moonscape" as Tongan families in New Zealand desperately seek news of the fate of their loved ones.
The ash cloud that soared 20km into the sky at the peak of Saturday's eruption is now moving across the Pacific, say experts, affecting the atmosphere and sunsets in countries such as Fiji, Vanuatu and - possibly from today - parts of Australia.
The eruption and resulting tsunami waves have cut power and communication to Tonga and water has been contaminated by the ash from the massive explosion of the Hunga Tonga-Hunga Ha'apai undersea volcano, 65km from the Tongan capital, Nuku'alofa.
So far, there have been no confirmed injuries or casualties, although there are reports of at least two people missing.
Auckland's Tongan community is desperate for news of loved ones back home and many spent yesterday in vain trying to contact them after the eruption rocked the island kingdom.
As New Zealand prepares to help Tonga in its recovery - Prime Minister Jacinda Ardern has already committed an initial $500,000 - a New Zealand Navy vessel is on standby to provide assistance if required.
Update from Ha'apai - no casualties reported
Labour MP Jenny Salesa, a proud Tongan, told followers on Facebook late last night that she had just attended a Zoom meeting with a number of Tongan Methodist church ministers - including one based in Tonga.
"One of the updates was from Rev 'Ulufonua, from Ha'apai ... he informed us that there have been no lives lost in the main island of Ha'apai.
"Drinking water has been hugely affected, there is a lot of ash on the ground [and] quite a number of houses have been damaged."
'Ulufonua told the group they had not yet had any updates from the outer islands in Ha'apai.
"We still do not know the full extent of the damages. However, it is such wonderful news for now that there are no casualties that we know of yet," Salesa said.
Ash cloud spreads to Fiji, New Caledonia, Vanuatu and Samoa
MetService - one of nine Volcanic Ash Advisory Centres around the world - is monitoring the ash movement across the Pacific region.
Its role is to provide accurate and up-to-date information for aircraft and airlines to ensure safe operations after such an eruption.
Meteorologist Luis Fernandes said the ash had mostly dispersed in the last almost 48 hours since the eruption and had spread to other Pasifika countries.
Current imagery showed ash covering the whole of Tonga and is now affecting parts of Fiji, New Caledonia, Vanuatu and Samoa.
At this stage, it did not look as if it will reach New Zealand, he said.
The explosion, just after 5pm on Saturday, was heard about two hours later in New Zealand as the sound spread across the Pacific.
"It was like distant cannons, a popping sound ... quite surreal because beautiful blue sky on a summer day, and you could hear like fireworks a long, long way away," said Auckland resident Brian Hamilton.
Hamilton was hard of hearing and only caught the louder ones, but his wife heard more. "You could feel it in your eardrums."
He is one of thousands across New Zealand who heard the submarine volcano exploding more than 2000km away.
Social media was abuzz with people posting from Auckland, Tauranga, Napier, Wellington, and far south as Invercargill.
Hunga's eruption injected a huge amount of energy into the atmosphere, said Richard Easther, professor of physics at the University of Auckland. "The bigger the explosion, the more air is stirred up, so the louder it's going to be.
"It's not one continuous wall of sound, it's a pulse of sound that works its way out, spreads out effectively as a circle centred on the volcano."
People in the North Island would have heard it before people in the South Island.
Sound travels about one kilometre every three seconds, so what New Zealanders heard would have taken place about two hours earlier in Tonga, some 2400km away, estimates Dr Marcus Wilson, senior lecturer in physics at the University of Waikato.
A single blast would disperse as the sound travels, arriving as a lasting rumble that can take many seconds to pass. "It will be the really low sounds you're hearing, a really deep rumbling."
One Auckland man's family has managed to make contact with a relative in the capital, Nuku'alofa, who described the island as being "covered in volcanic ash" after Saturday evening's eruption.
Sola Vuna, a teacher at Manurewa High School, said his family only got a brief message back from the relative late yesterday morning.
He described the main seaside road — Vuna Rd — as covered with debris from the sea. Communication lines remained down last night.
'I can't sleep properly. You go to sleep thinking of them'
Auckland Tongan community leader Salote Heleta-Lilo told the Herald they were still trying desperately to get news from her sister who lives at the family home in Nuku'alofa and takes care of an elderly uncle, who is paralysed.
"It's a concern because they're right on the coast there. It's quite sad - living in fear and not knowing what's happened in Tonga," she said.
Heleta-Lilo said she believed their house will be severely damaged if not destroyed as a result. But that was not the main worry at the moment.
"The house is materialistic. I'm just concerned for their lives.
"I can't sleep properly. You go to sleep just thinking of them."
Heleta-Lilo, who was born and raised in Tonga, said she had never seen anything like the eruption in her lifetime.
Speaking to a cousin in Hawaii yesterday, she was shocked to hear him describe rocks raining from the sky after the eruption.
"He said there were little stones raining outside. That's how scary it is - it shows how big it was."
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The relative also reported that the wharf on 'Eua island was badly damaged and there were fears for those on the small islands of Nomuka and Atatā, two of the closest to the Hunga Tonga-Hunga Ha'apai volcano which sent ash, steam and gas up to 20km into the air on Saturday and a tsunami and surging swells around Tonga and the wider Pacific.
Vuna Rd also runs past the royal palace, which was evacuated. King Tupou VI was among the members evacuated.
Vuna said efforts to contact relatives in the kingdom spanned cousins in America, Australia and around New Zealand making calls to various phone numbers and Facebook pages.
"We've all been trying and we're still trying," he said last night.
"My Mum's brother and sister and cousins are all in Tonga and my Dad — his two older brothers are there."
Vuna said his elderly parents, Salome and Filimone, had been up all night Saturday praying and listening to the Tongan radio station for updates.
"There was an online prayer session [on Saturday] night. Mum's been crying and singing and crying again."
Auckland Tongan community leader Melino Maka said not knowing what was happening was the worst part.
"I've even tried calling some of the ministers I know there through their direct personal phones — no luck at all."
It's believed ash cloud from the underwater volcano has contaminated Tonga's water supplies and sparked fears the air was toxic.
Iliesa Tora, who moved on Saturday night to higher ground on Tonga's largest island, Tongatapu, described rocks showering down as he and his family drove to safety.
"Small rocks from the volcanic eruption started to fall like rain," he said in a video posted to social media translated into English by the Fiji Times.
New Zealand's Acting High Commissioner to Tonga Peter Lund told TVNZ that Tonga's capital Nuku'alofa looks "like a moonscape" after being blanketed in volcanic ash. He said there was a lot of damage on the Nuku'alofa waterfront, and the western coast was "pummeled quite badly".
"Thankfully we're not facing devastation on a mass scale but there will be some serious issues to address given what the volcanic ash has done to the soil and the land."
Lund said there were reports of people being unaccounted for.
There had been no official reports of injuries or deaths but yesterday Prime Minister Jacinda Ardern said satellite images "brought home the scale and the violence of that eruption" and that videos of the tsunami's surge would have been "hugely concerning" those who saw them.
Ardern committed to providing Tonga with whatever help it needed. Initial requests were for water because of contamination of existing supplies from volcanic ash, she said.
An initial $500,000 of aid has been committed by New Zealand as "a starting figure".
Ardern urged New Zealanders in Tonga to keep family informed of their wellbeing.
Pacific Peoples Minister Aupito William Sio said those with links to Tonga were understandably worried.
"The Pacific are part of our family and so there's been overwhelming concern from the diaspora here."
Saturday night's swells spread around the Pacific but hit hardest in New Zealand at Northland's Tutukaka Marina, causing millions of dollars of damage to boats and facilities. Between 50 and 60 vessels were damaged and around a dozen were sunk.
Tsunami advisories were issued for Japan, Hawaii, Alaska and the US Pacific coast. Authorities in Southern California closed beaches and piers as a precaution.
- Additional reporting: George Clark, Northern Advocate