The first flights from Australia and New Zealand landed in Tonga on Thursday with much-needed supplies of water for sanitation and hygiene as well as shelter, communication equipment and power generators.
A New Zealand maritime sustainment vessel HMNZS Aotearoa carrying 250,000 litres of water and able to produce 70,000 litres per day through a desalination plant, is expected to arrive in Tonga on Friday.
A second Australian aid flight had to turn back on Thursday due to in-flight issues and is now expected later on Friday, the Australian High Commission in Tonga said on Facebook.
More help is on the way with HMAS Adelaide en route from Brisbane and due in Tonga next week, it said.
The Hunga Tonga-Hunga Ha'apai volcano erupted with a deafening explosion on Saturday, triggering tsunamis that destroyed villages, resorts and many buildings and knocked out communications for the nation of about 105,000 people.
Three people have been reported killed, authorities said.
Ash has blanketed the archipelago and spoiled much of its drinking water.
United Nations spokesman Stephane Dujarric said in a briefing that Tonga has asked for urgent assistance and the agency is in close contact with the authorities.
Some 60,000 people have been affected by damage to crops, livestock, and fisheries due to ashfall, saltwater intrusion and the potential for acid rain. There are also reports of fuel shortages.
Australia's foreign minister Marise Payne on Friday said cash donations to Tonga for immediate humanitarian supplies - Australia has donated $1 million - would need to be followed with more substantial support for rebuilding.
Telephone links between Tonga and the outside world were reconnected late on Wednesday, although restoring full internet services is likely to take a month or more.
Tongans have turned to social media to post images of the destruction by the tsunami and give accounts of their shock after the massive explosion.
In a radio address, Tonga King Tupou VI urged courage and hard work for the rebuilding process.
The king also received a message of condolence on Thursday from Queen Elizabeth, who said she was "shocked and saddened" by the devastation.
"It must be incredibly difficult for those who are unable to contact friends and family while communications are disrupted, and I hope that they will soon be restored," the Queen said.
NASA's Goddard Space Flight Center has said the force of the eruption was estimated to be the equivalent of five to 10 megatons of TNT, or more than 500 times that of the nuclear bomb the United States dropped on the Japanese city of Hiroshima at the end of World War II.
