The International Federation of Red Cross and Red Crescent Societies (IFRC) said that with the extra supplies, its staff and volunteers were stepping up deliveries of drinking water and setting up shelters across the country's many islands.

"This disaster has shaken the people of Tonga like nothing we have seen in our lifetime," Sione Taumoefolau, secretary-general of Tonga Red Cross, said in a statement on Wednesday.

"The tsunami has wiped out homes and villages, but we are already rebuilding amid the ashes."

The US Agency for International Development said the United States was providing an additional $US2.5 million in humanitarian assistance and the guided-missile destroyer USS Sampson, part of a multinational effort, arrived this week to support the efforts in Tonga.

An Australian warship was arriving to coronavirus-free Tonga Wednesday evening, delivering aid without human contact after about two dozen cases of COVID-19 have been recorded among the crew.

Broadcom Broadcasting radio cited Tonga's Health Minister Saia Piukala as saying 29 positive cases had been reported aboard HMAS Adelaide, but all the positive personnel were asymptomatic.

"The ship will berth and no contacts will be made," Piukala said. "Australians from the ship will unload their cargoes and sail from port."

The United Nations, Red Cross and other relief agencies on the ground in Tonga have warned that a COVID-19 outbreak in the island would be catastrophic at this time.

"There is an urgent need for people to have access to safe water sources in the days and weeks to come," Taumoefolau said.

"Ash has settled in water tanks, requiring time to settle and careful treatment before use. It has also smothered much of the country, including houses and crops."

The Hunga Tonga-Hunga Ha'apai volcano eruption triggered a tsunami that destroyed villages and resorts and knocked out communications for the nation of about 105,000 people. Three people had been reported killed, authorities said.

Australian Associated Press