An estimated one cubic kilometre of material blasted from the volcano, and experts expect Hunga-Tonga-Hunga-Ha'apai to remain active "for weeks to months".
"Tonga's people are going to need sustained support responding to a disaster of this scale," Sione Hufanga, the United Nations Coordination Specialist in Tonga said.
"The people of Tonga are still overwhelmed with the magnitude of the disaster."
Tonga ranks third on the World Risk Report, which measures countries on their susceptibility to experiencing natural disasters.
But, despite the risk, Kupu said most Tongans wanted to stay.
"It's this feeling of pride that we have here, that we don't want to leave the country we were born and raised in," she said.
One survivor from the island of Atata, which was flattened by the tsunami, told her he would return to the island even after the devastation, she added.
"He explained he wished to go back because his parents are buried there, he was born there and his life is there. He wished the government or anybody would help rebuild his little island so he could go back."
The New Zealand and Australian defence forces have started delivering urgent relief supplies, particularly water, to Tonga but an Australian minister said fears of unleashing a "Covid crisis" were complicating aid efforts.
Tonga is Covid-free and has strict border control policies, requiring contactless delivery of aid, and a three week quarantine period for any aid personnel who wish to enter the country.
"It's a very, very difficult time for the people of Tonga," Australia's international development minister Zed Seselja said, but added: "We respect absolutely the desire of the Tongan government not to add a Covid crisis to a humanitarian crisis caused by a tsunami."
Meanwhile a third New Zealand navy vessel carrying helicopters, water, tarpaulins, milk powder and engineering equipment is on its way to Tonga and is expected to arrive early next week.
Defence minister Peeni Henare said all deliveries will be contactless in accordance with Tonga's Covid-19 protocols.
The Tongan government has called the dual eruption-tsunami "an unprecedented disaster" and declared a nearly one-month national emergency.
The eruption broke a vital undersea communications cable linking Tonga with the rest of the world, and it is expected to be at least a month before all communication services are fully restored.
In the meantime partial communications has been established, although mobile network provider Digicel said the high number of calls to the island was producing delays.