New images taken by the New Zealand defence force have revealed the devastation caused after a volcano erupted near Tonga.
A huge cloud of black ash that has settled on Tonga is hampering rescue efforts as have downed communications with outlying islands.
The region has suffered major damage from the volcanic eruption and tsunami, said the United Nations.
Tonga police have said the death toll stands at two but with communications in the South Pacific island nation cut, it is difficult to have a clear figure.
Tonga's main airport, Fua'amotu International Airport, was not damaged in Saturday's eruption and tsunami but heavy ashfall is preventing full operations, hampering international relief efforts.
"The priority now will to be get supplies to Tonga, and the biggest constraint on that at the moment ... is the airport. There is still a significant amount of ash," Australia's Minister for the Pacific Zed Seselja said.
Tongan officials were planning to evacuate people from outer islands where conditions were "very tough, we understand, with many houses being destroyed in the tsunami", Seselja said.
The UN said a distress signal was detected in an isolated, low-lying Ha'apai islands group, adding it had particular concerns about Fonoi and Mango islands.
According to the Tonga government, 36 people live on Mango and 69 on Fonoi.
The Tongan navy reported major damage in the Ha'apai islands which were hit by waves estimated to be 5-10 metres high, said the UN.
Surveillance images taken by the New Zealand defence force and circulated on social media in Tonga showed "catastrophic damage" to the outlying island of Atata.
The islands of Fonoifua, Niniva, Nomuka and Mango all had damage ranging from extensive to catastrophic, with an entire village destroyed on Mango.
Tonga is a kingdom of 176 islands, of which 36 are inhabited, with a population of 104,494 people.
The Hunga Tonga-Hunga Ha'apai volcano, which sits on the seismically active Pacific Ring of Fire, is about 40 miles north of Tonga's capital.
The eruption sent tsunami waves across the Pacific Ocean and was heard 1,430 miles away in New Zealand.
The South Pacific archipelago had its main undersea communications cable cut by the impact of the eruption hampering rescue efforts as a thick layer of ash blankets the islands, the New Zealand High Commission said.
It added it was working to establish communications with smaller islands "as a matter of priority".
One victim was Brit Angela Glover, 50, who was killed in the tsunami as she tried to rescue dogs she looked after at a rescue shelter, her brother said, the first known death in the disaster.
"We don't have any further information that would suggest ... significant casualties," Seselja told the Australian broadcaster Nine's Today show.
The airport was likely to be open by Wednesday, he said.
Tonga's deputy head of mission in Australia, Curtis Tu'ihalangingie, said Tonga was worried that aid deliveries could spread Covid to the virus free nation.
"We don't want to bring in another wave - a tsunami of Covid-19," Tu'ihalangingie said, urging the public to wait for a disaster relief fund to donate.
Any aid sent to Tonga would need to be quarantined, and it was likely no foreign personnel would be allowed to disembark aircraft, he said.
The Red Cross said it was mobilising its network to respond to what it called the worst volcanic eruption the Pacific has
experienced in decades.
Alexander Matheou, the Red Cross' Asia Pacific director, said water purification to remove ash contamination, providing
shelter and reuniting families were the priorities.
"Further volcanic activity cannot be ruled out," said the UN's Office for the Coordination of Humanitarian Affairs.
The impact of the huge eruption was felt as far away as the United States. Two people drowned off a beach in Peru due to high waves caused by the tsunami, while officials in Japan reported several evacuations.
The island of Hunga-Tonga-Hunga-Ha'apai all but disappeared following the blast, according to satellite images taken about 12 hours later, making it difficult for volcanologists to monitor activity.
Experts said the volcano, which last erupted in 2014, had been puffing away for about a month before Saturday's eruption.
