This satellite image shows an undersea volcano eruption at the Pacific nation of Tonga on Saturday. AP

The tsunami threat around the Pacific from a huge undersea volcanic eruption began to recede Sunday, while the extent of damage to Tonga remained unclear.

An underwater volcano off Tonga erupted on Saturday, triggering a tsunami on the shores of Tonga and cutting off phone and internet lines for the entire island.

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There are no official reports of injuries or deaths in Tonga as yet but communications are still limited and outlying costal areas remain cut off.

Satellite images showed the spectacular eruption that took place Saturday evening, with a plume of ash, steam and gas rising like a mushroom above the blue Pacific waters. A sonic boom could be heard as far away as Alaska.

An aerial view shows capsized boats in Muroto, Kochi prefecture, Japan. Reuters

In Tonga it sent tsunami waves crashing across the shore and people rushing to higher ground.

A New Zealand Air Force P-3K Orion aircraft left from Auckland on Monday to assist in an initial impact assessment of the area and low-lying islands, the New Zealand defence forces said on Twitter.

New Zealand's Prime Minister Jacinda Ardern said on Sunday that the tsunami had a significant impact on infrastructure.

The eruption cut the internet to Tonga, leaving friends and family members around the world anxiously trying to get in touch to figure out if there were any injuries and the extent of the damage. Even government websites and other official sources remained without updates on Sunday afternoon.

Dave Snider, the tsunami warning coordinator for the National Tsunami Warning Center in Palmer, Alaska, said it was very unusual for a volcanic eruption to affect an entire ocean basin, and the spectacle was both "humbling and scary.”

Tsunami from underground volcano near Tonga hits the Small Craft Harbor in Santa Cruz, California. AP

The tsunami waves caused damage to boats as far away as New Zealand and Santa Cruz, California, but did not appear to cause any widespread damage. Snider said he anticipated the tsunami situation in the US and elsewhere to continue improving.

Tsunami advisories were earlier issued for Japan, Hawaii, Alaska and the US Pacific coast.

The US Geological Survey estimated the eruption caused the equivalent of a magnitude 5.8 earthquake. Scientists said tsunamis generated by volcanoes rather than earthquakes are relatively rare.