The tsunami threat around the Pacific from a huge undersea volcanic eruption began to recede on Sunday.
But the extent of damage to Tonga remained unclear, after tsunami waves crashed across the coast and forced people to flee to higher ground, AP reported.
Satellite images showed the eruption that took place on 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.
The eruption cut the internet to Tonga, leaving friends and family members around the world anxiously trying to get in touch. Government websites and other official sources remained without updates on Sunday.
Tonga gets its internet via an undersea cable from Suva, Fiji. All internet connectivity with Tonga was lost at about 6.40pm local time, said Doug Madory, director of internet analysis for the network intelligence firm Kentik.
There have not yet been any official reports of injuries or deaths in Tonga, New Zealand Prime Minister Jacinda Ardern said. Authorities have yet to make contact with some coastal areas and smaller islands.
“Communication with Tonga remains very limited,” Ms Ardern said. “And I know that is causing a huge amount of anxiety for the Tongan community here.”
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, contaminating water supplies and making freshwater a vital need.
Aid agencies said thick ash and smoke had prompted authorities to ask people to wear masks and drink bottled water.
New Zealand was unable to send a military surveillance flight over Tonga on Sunday because the ash cloud was 19,000 metres high but it hoped to send the flight on Monday, followed by supply planes and navy ships, Ms Ardern said.
One complicating factor to any international aid effort is that Tonga has so far managed to avoid any outbreaks of Covid-19.
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.
Dave Snider, the tsunami warning co-ordinator 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.
Tsunami advisories were earlier issued for Japan, Hawaii, Alaska and the US Pacific coast.
The Tonga Meteorological Services said a tsunami warning was declared for all of the archipelago, and data from the Pacific tsunami centre said waves of 80 centimetres were detected.
New Zealand scientist Marco Brenna, a senior lecturer at Otago University's School of Geology, described the impact of the eruption as "relatively mild" but said another eruption with a much bigger impact could not be ruled out.
US Secretary of State Antony Blinken wrote on Twitter that he was “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”.
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.”
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 and to pay attention to instructions from their local emergency management officials.
Police rescued a surfer whose board broke in powerful waves off San Francisco.
In Southern California, surging waters sank at least one boat in the Ventura Harbour north-west of Los Angeles.