WELLINGTON - A massive volcanic eruption in Tonga that triggered tsunami waves around the Pacific caused "significant damage" to the island nation's capital and smothered it in dust, but the full extent was unclear with communications still hampered Monday.

The eruption on Saturday was so powerful it was recorded around the world and heard as far away as Alaska, triggering a tsunami that flooded Pacific coastlines from Japan to the United States.

The capital Nuku'alofa suffered "significant" damage, New Zealand Prime Minister Jacinda Ardern said, adding there had been no reports of injury or death but a full assessment was not yet possible with communication lines down.

"The tsunami has had a significant impact on the foreshore on the northern side of Nuku'alofa with boats and large boulders washed ashore," Ardern said after contact with the New Zealand embassy in Tonga.

"Nuku'alofa is covered in a thick film of volcanic dust but otherwise conditions are calm and stable."

Tonga was in need of water supplies, she said, as "the ash cloud has caused contamination."

There has been no word on damage in the outer islands but New Zealand sent an air force reconnaissance aircraft early Monday "to assist in an initial impact assessment of the area and low-lying islands," the country's Defence Force said.

Tonga has also accepted Canberra's offer to send a surveillance flight, Australia's foreign office said, adding it is also immediately prepared to supply "critical humanitarian supplies".

The United States and the World Health Organization have pledged support, while the United Nations children's agency said it was preparing emergency supplies to fly in.

A 1.2-meter wave swept ashore in the Tongan capital with residents reporting they had fled to higher ground, leaving behind flooded houses, some with structural damage, as small stones and ash fell from the sky.

"It was massive, the ground shook, our house was shaking. It came in waves. My younger brother thought bombs were exploding nearby," resident Mere Taufa told the Stuff news website Saturday.

She said water filled their home minutes later and she watched the wall of a neighboring house collapse.

"We just knew straight away it was a tsunami. Just water gushing into our home," Taufa said.

"You could just hear screams everywhere, people screaming for safety, for everyone to get to higher ground."