Wellington: The tsunami threat around the Pacific from a huge undersea volcanic eruption began to recede Sunday, but the massive ash cloud covering the tiny island nation of Tonga prevented surveillance flights from New Zealand to assess the extent of damage.

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.

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

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. Even government websites and other official sources remained without updates on Sunday afternoon.

New Zealand Prime Minister Jacinda Ardern said there had not yet been any official reports of injuries or deaths in Tonga, but cautioned that authorities hadn't yet made contact with some coastal areas and smaller islands.

Communication with Tonga remains very limited. And I know that is causing a huge amount of anxiety for the Tongan community here, Ardern said.

She said there had been significant damage to boats and shops along the Tongan coastline. The capital, Nuku'alofa, was covered in a thick film of volcanic dust, Ardern said, contaminating water supplies and making fresh water a vital need.

Aid agencies said thick ash and smoke had prompted authorities to ask people to wear masks and drink bottled water.

Ardern said New Zealand was unable to send a surveillance flight over Tonga on Sunday because the ash cloud was 63,000 feet (19,000 metres) high but they hoped to try again on Monday, followed by supply planes and navy ships.

One complicating factor to any international aid effort is that Tonga has so far managed to avoid any outbreaks of COVID-19. Ardern said New Zealand's military staff were all fully vaccinated and willing to follow any protocols established by Tonga.

Dave Snider, the tsunami warning coordinator for the National Tsunami Warning Centre 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 .

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.

Rachel Afeaki-Taumoepeau, who chairs the New Zealand Tonga Business Council, said she hoped the relatively low level of the tsunami waves would have allowed most people to get to safety, although she worried about those living on islands closest to the volcano. She said she hadn't yet been able to contact her friends and family in Tonga.

We are praying that the damage is just to infrastructure and people were able to get to higher land, she said.

US Secretary of State Antony Blinken wrote on Twitter he is deeply concerned for the people of Tonga as they recover from the aftermath of a volcanic eruption and tsunami. The United States stands prepared to provide support to our Pacific neighbours .

Tonga gets its internet via an undersea cable from Suva, Fiji. All internet connectivity with Tonga was lost at about 6:40 pm local time Saturday, said Doug Madory, director of internet analysis for the network intelligence firm Kentik.

On Tonga, which is home to about 105,000 people, video posted to social media showed large waves washing ashore in coastal areas and swirling around homes, a church and other buildings. A Twitter user identified as Dr Faka'iloatonga Taumoefolau posted video showing waves crashing ashore.

Can literally hear the volcano eruption, sounds pretty violent, he wrote, adding in a later post: Raining ash and tiny pebbles, darkness blanketing the sky.

The explosion of the Hunga Tonga Hunga Ha'apai volcano, about 64 km (40 miles) north of Nuku'alofa, was the latest in a series of dramatic eruptions. In late 2014 and early 2015, eruptions created a small new island and disrupted international air travel to the Pacific archipelago for several days.

Earth imaging company Planet Labs PBC had watched the island in recent days after a new volcanic vent began erupting in late December. Satellite images showed how drastically the volcano had shaped the area, creating a growing island off Tonga.

The surface area of the island appears to have expanded by nearly 45% due to ashfall, Planet Labs said days before the latest activity.

Following Saturday's eruption, residents in Hawaii, Alaska and along the US Pacific coast were advised to move away from the coastline to higher ground.

Savannah Peterson watched in shock as the water rose several feet in a matter of minutes in front of her oceanfront house in Pacifica, California, just south of San Francisco.

It came up so fast, and a few minutes after that it was down again. It was nuts to see that happen so quickly, she said. I've never had water come all the way up to my front door, and today it did.

Police rescued a surfer whose board broke in powerful waves off San Francisco. In Southern California, surging waters sunk at least one boat in Ventura Harbour northwest of Los Angeles.