New Zealand has sent a plane to Tonga to assess the damage after a huge volcanic eruption triggered a tsunami.
The eruption has covered the Pacific islands in ash, cut power and severed communications.
Up to 80,000 people there could be affected, the International Federation of Red Cross and Red Crescent Societies (IFRC) said.
New Zealand Prime Minister Jacinda Ardern said the tsunami had wreaked “significant damage”.
Information remains scarce, however, and New Zealand and Australia are sending surveillance flights to assess the extent of the damage.
The New Zealand Defence Force tweeted that an aircraft had left to “assist in an initial impact assessment of the area and low-lying islands”.
Katie Greenwood of the IFRC in Fiji said that help was urgently needed.
“We suspect there could be up to 80,000 people throughout Tonga affected by either the eruption itself or from the tsunami wave and inundation as a result of the eruption,” she said.
“That was a shock to people, so we do hold some concern for those outer islands and we’re very keen to hear from people.”
The underwater volcano erupted on Saturday, sending a plume of ash into the sky and triggering warnings of 1.2m waves reaching Tonga. The eruption was so loud it could be heard in New Zealand, some 2,383km from Tonga.
New Zealand’s Acting High Commissioner in Tonga Peter Lund has said the island nation looks “like a moonscape” after it was coated in a layer of volcanic ash.
The dust was reportedly contaminating water supplies and making fresh water a vital need, Ms Ardern said on Sunday.
Aid charities said the ash had prompted authorities to tell people to drink bottled water and wear face masks to protect their lungs.
As the sky darkened with ash, videos showed traffic jams as people fled low-lying areas by car. Hours later, Tonga’s internet and phone lines went down, making the island’s 105,000 residents almost entirely unreachable.
Prior to the largest eruption, the volcano had been erupting for several days. The Tonga Meteorological Agency had warned that the smell of sulphur and ammonia was being reported in some areas.
Ms Ardern said power was being restored to some parts of the island and mobile phones were slowly starting to work again. But the situation in some coastal areas remained unknown.
Satellite images suggest some outlying islands have been completely submerged by seawater.
Experts say the eruption of the Hunga-Tonga Hunga-Ha’apai volcano is one of the most violent in the region in decades.
It triggered tsunami warnings in several countries, including Japan and the US, where flooding hit some coastal parts of California and Alaska.