Tonga's government says drinking water is the priority, and a national emergency team has already distributed 60,000 litres of water to residents.
A desalination plant on a New Zealand naval ship that arrived on Friday, capable of producing 70,000 litres a day, has started drawing sea water from Tonga's harbour.
Residents who had lost homes on outlying islands when a tsunami reaching up to 15 metres crashed over the South Pacific archipelago would be relocated to the main island, Tongatapu, because of water and food shortages, the Tongan prime minister's office said.
Volcanic fallout on the surface of the ocean was damaging boats and making marine transport between the islands challenging, and domestic flights were suspended, it said.
Ash fall and the tsunami had affected 84 per cent of the population, and inter-island communications remained an "acute challenge" with limited satellite and radio links, it said.
Burials were held earlier in the week for a Tongan man and a woman who had died when the tsunami hit the outlying Ha'apai islands.
The official death toll is three. A field hospital has been set up on Nomuka Island after the health centre there was swept away.
Faka'iloatonga Taumoefolau, the co-ordinator for the project to rebuild Tonga's parliament, said the restoration of international money transfer services, for limited hours on Saturday, was important for people to be able to buy essential goods.
"Tongans have demonstrated their resilience in this calamity and will get back on their feet," he said, speaking to Reuters from Tongatapu.
More naval vessels from Australia, New Zealand and Britain are on the way to Tonga to deliver aid. Two aid flights, from Japan and New Zealand, arrived on Saturday with humanitarian supplies, after two flights from Australia on Friday evening.
The Tongan government has implemented a strict COVID-19 policy that means people, including aid workers, cannot enter the country unless they have undergone a three-week isolation period.
Aid deliveries have been contactless, with pallets quarantined for 72 hours after arrival at the airport before being distributed by Tongan authorities. One Australian aircraft returned to Brisbane midflight on Thursday after being notified of a COVID-19 case among the crew.
An aid delivery expected from China would also be contactless, the government said.
An Australian navy vessel, HMAS Adelaide, was expected to arrive in Tonga on Wednesday with more bulk water and a 40-bed field hospital, Australia's minister for international development and the Pacific, Zed Seselja, told reporters in Canberra on Saturday.
Australia and New Zealand were co-ordinating an international aid effort with support from Britain, France, the United States, Fiji and Papua New Guinea, he said, and the Tongan government had asked for support to be paced so the small airport was not overwhelmed.
Asked by reporters about China's aid program in the Pacific, Seselja said: "We welcome offers of support from anyone, including the Chinese government."
The Tongan government said it was "deeply appreciative to the international community" for its assistance, which included $US8 million ($A11 million) in funding from the World Bank and $US10 million from the Asia Development Bank.
Reliance, a repair ship due to reconnect the undersea cable that links Tonga to international telecoms networks, left its Port Moresby mooring and was expected in Tonga on January 30, according to Refinitiv data on shipping movements.
