Tongan Prime Minster Siaosi Sovaleni said all houses on the island of Mango, where 36 people live, were destroyed.

Only two houses remain on Fonoifua island, and extensive damage was reported on Nomuka island, home to 239 people, he said.

"An unprecedented disaster hit Tonga," Sovaleni said, adding a "volcanic mushroom plume" extended to cover all of the country's roughly 170 islands -- of which 36 are inhabited -- impacting the entire population of more than 100,000 people.

A United Nations spokesperson said an initial assessment by Tongan authorities found 100 houses were damaged and 50 destroyed on Tongatapu, the country's main island, home to the majority of the population.

No evacuation centers are open on the main island, and people who were displaced are mostly staying with extended families.

On 'Eua, 89 people are in evacuation centers, the spokesperson said, adding that information from outer islands remains scarce.

Race to deliver aid to Tonga

The first details of the devastation emerged on Tuesday after Tonga's Pacific neighbors, Australia and New Zealand, made reconnaissance flights to the archipelago -- a three- to five-hour journey.

Photos show entire island communities that were once lush and green, now blanketed by thick, gray ash.