Australia and New Zealand have readied their warships with medical and engineering equipment for humanitarian assistance and disaster relief (HADR) operations in Tonga.
Tonga's communications and infrastructure were damaged by a tsunami triggered by an underwater volcano eruption on 15 January.
The "unprecedented disaster" triggered a mass evacuation.
"The Government of Tonga requested the flights to help determine the extent of the damage, particularly in more remote locations, and inform their future disaster support requests," Australia's Department of Defense said.
Australia's Canberra-class landing helicopter dock (LHD) ship Adelaide, which can operate in shallower waters, is also being loaded in Brisbane with medical and engineering equipment and personnel. It will take five days to travel to Tonga.
Australia's Foreign Minister Marise Payne said that HMAS Adelaide would act as a base for Australian helicopters to service populations on outer islands such as Mango, Fonoi, and Atata.
Tonga's Mango and Atata Islands are 50-70 km away from the Hunga Tonga-Hunga Ha'apai volcano. Atata has a population of about 100 people and Mango around 69 people.
Images showed that on Atata, many buildings are either underwater or have been washed away by the tsunami. A general intelligence assessment (GIA) said Mango Island experienced "catastrophic" damage.
"You can see on the images quite a wave of devastation across infrastructure and houses there," Peeni Henare, New Zealand's defence minister, said on Tuesday.
In its first statement since the disaster, the Tongan government said on Tuesday that all houses have been destroyed on Mango Island, while only two houses remain on Fonoifua Island.
"To date, there are three confirmed fatalities including a British national; a 65-year-old female from Mango Island; and a 49-year-old male from Nomuka island. There are also a number of injuries reported," the government's statement read.
Payne called the damage to the island nation "absolutely devastating" and said that New Zealand and Australia would provide support to the Tongan government.
New Zealand's HMNZS Wellington sailed from Devonport Naval Base with personnel, equipment, and supplies to assist the rescue and cleanup efforts.
HMNZS Wellington, an Offshore Patrol Vessel, is designed for maritime surveillance, supply and support, and patrol missions around New Zealand’s 15,000-kilometre coast, the Southern Ocean, and the Pacific.
"The ship is carrying divers and hydrographers from HMNZS Matataua to survey shipping channels and ports and has a Seasprite helicopter on board to assist with supply delivery," New Zealand's Defence Forces said.
The World Health Organisation (WHO) advised Tongan people to remain indoors as ash in the air and on the ground has raised serious health concerns about air pollution and the potential contamination of food and water supplies.