The New Zealand Defence Force's Commander of Joint Forces says an air force C-130 Hercules arrived in Tonga just after 4pm today, following a "mammoth effort" by Tongan armed forces to clear the Tongatapu airport runway by hand.
Rear Admiral Jim Gilmour said the airport at Tongatapu, in Nuku'alofa, was heavily covered in ash until today.
"There was a mammoth effort by His Majesty's armed forces to clear that runway by hand," Gilmour said.
An NZDF plane with MFAT relief supplies arrived shortly after 4pm, he said.
"No-contact Covid protocols are being adhered to rigorously."
The aircraft will return to New Zealand tonight and will be on standby for another task as soon as Saturday.
A look at Nuku'alofa airport from a surveillance flight showed that structures there did not appear to be damaged, he said.
"We'll get a report back from the Hercules crew shortly, I would expect, on just what the facilities are like on the ground."
Gilmour said the images so far out of Tonga had been "worrying", but the current understanding of the impact of the damage was insufficient to comment on what would be required next in terms of assistance.
HMNZS Wellington, which departed on Tuesday, is expected to arrive in Tongatapu this evening to commence a survey of the harbour.
"We were also aware that there was going to be some disruption to the Nuku'alofa harbour in other areas and this is going to be a key method of entry to the country ... So we were aware that getting a ship away with a hydrographic and diving team would be important, we were also aware that water, food, hygiene, shelter - all those basic needs - were going to be threatened."
The volcanic eruption caught everyone by surprise, Gilmour said.
"We took time and energy on that Saturday evening to ensure that defence force assets were prepared for the tsunami that arrived here and then got on the business on Sunday of doing our best to understand the situation in Tonga and wider Pacific region as a result," Gilmour said.
"Within our hearts, as with everyone else in New Zealand, we were very worried about the fate of the people in Tonga and further afield, it's a massive detonation."
There were still three confirmed deaths, but he added: "From the size of that explosion that could be seen from orbit and the tsunami that was felt and experienced all the way across the Pacific, sadly I would be very surprised if there were not more injuries, but we'll just have to get there to find out."
Initial surveillance images on Monday from an NZDF plane were passed on to the Tongan government.
Another flight on Wednesday was also conducted to help understand the situation on the ground, he said.
"The images that were taken on the second flight yesterday - there was a couple of objectives for that surveillance flight yesterday ... to have a look at the eastern border of the Lau group [of islands] in Fiji after Cyclone Cody, so we did that on the way and happily there was no damage observed through any of that surveillance.
"Across the Tongan group, we were keen to close off some of the gaps we had from the first surveillance flight and also in response to some specific request for information from the Tongan government and also to revisit some areas to get some better imagery, plus do a survey particularly of airfield and port infrastructure in the northern island groups to facilitate our expectations of how we might operate in the coming days."
Earlier today, Defence Minister Peeni Henare announced a third navy ship will be sent to sent to Tonga tomorrow to aid in the relief efforts following the weekend's eruption of the Hunga-Tonga-Hunga-Ha'apai volcano.
Arriving tomorrow is HMNZS Aotearoa, which has up to 250,000 litres of fresh water and relief supplies.
HMNZS Canterbury has not been requested yet, but Gilmour said it was anticipated her capabilities would be required so the vessel would be loading cargo tomorrow and head off for Tonga then.
"This will be not an intention of getting in front of permissions or asks from the Kingdom of Tonga, our thinking is it's much better to get the capability 15 miles off the coast of Tonga and be turned around, than to be desperately required and still here in New Zealand."
HMNZS Canterbury is expected to depart tomorrow night or Saturday morning at latest, and should arrive about Tuesday, Gilmour said. It will carry relief supplies, desalination plants, helicopters, and engineers.
At this stage, there is no intention to load off any of that equipment on HMNZS Canterbury because it will first require permission from the Tongan government.
Late last night WHO liaison officer in Tonga Dr Yutaro Setoya, who is in Nuku'alofa, confirmed the Fua'amotu International Airport runway had been cleared of ash.