The first aerial images of the damage from the undersea volcanic eruption have been released by the Tongan government.
The island of Nomuku, which is one of the closest to the volcano, has "extensive" damage. And on Mango Island, where a distress signal has been activated, the destruction is called "catastrophic".
At Ha'apai, homes and the wharf have been demolished.
"You can see on the images quite a wave of devastation across infrastructure and houses there," says New Zealand Defence Minister Peeni Henare.
The images, taken by a New Zealand Air Force Orion, show ash covering the runway, making it difficult to get help to Tonga by air.
The HMNZS Aotearoa is loading up and the crew boarded on Tuesday afternoon to sail.
It'll follow the HMNZS Wellington, which is equipped with specialist gear to map the seafloor to see what obstructions exist in the Nuku'alofa harbour.
"So we'd get our hydrographic survey team to be involved. We'd expect that helicopters would be useful so we'd look to have helicopters ready to go if they're needed," says Joint Forces Commander Rear Admiral Jim Gilmour.
It comes amid confirmation of the first deaths.
Angela Glover's life in Tonga was all about rescuing and caring for unwanted dogs. But as the tsunami hit, the 50-year-old from Brighton, in the United Kingdom, went back to save her dogs, only to be swept out to sea. Her body has since been found.
"I will miss her and I will think of her every day until the day I die. You know, my mother is just broken at the moment. She is just absolutely shattered," says Angela's brother, Nick Eleini.
She's survived by her husband James, who managed to cling to a tree as the waves hit.
"Angela was the heart of our family, the emotional heart of our family," Nick adds.
Satellite images show a village near the capital Nuku'alofa, before the eruption and after, blanketed in brown ash and debris.
The western part of the main island, closest to the volcano, has suffered significant damage.
The owners of the popular waterfront Ha'atafu Beach Resort say it's been "completely wiped out".
"The situation obviously on the west coast where there was a lot of destruction, I think people will still be requiring shelter in evacuation centres," says Peter Lund, New Zealand's acting High Commissioner in Tonga.
Lund says there have been reports of three deaths, but the Ministry of Foreign Affairs and Trade says only two are confirmed.
An Australian naval vessel is also on the move and it's headed for Tonga with aid too, as the aftermath of this once-in-a-millennia blast is still being realised.
