The Hunga-Tonga-Hunga-Ha'apai volcano, about 18.6 miles southeast of Tonga's Fonuafo'ou island, first erupted on Friday and a second time on Saturday around 5:26 p.m. local time, according to CNN affiliate Radio New Zealand (RNZ).
The eruptions sent a plume of ash, gas and steam 12.4 miles into the air, according to RNZ. Satellite imagery showed a massive ash cloud and shockwaves spreading from the eruption. Ash was falling from the sky in the Tonga capital, Nuku'alofa, Saturday evening and phone connections were down.
The eruption caused a severe tsunami on Tongatapu, where the capital is located, with waves flowing onto coastal roads and flooding properties on Saturday.
So far, New Zealand authorities have not received any reports of deaths or injuries in Tonga related to the eruption, Prime Minister Jacinda Ardern said at a news conference on Sunday.
The tsunami had a "significant impact" on Nuku'alofa, with boats and large boulders washed ashore, and shops along the coast damaged, she added.
RNZ reported that residents fled for higher ground as waves swept the waterfront, main street and grounds of Tonga's Royal Palace. Though it was early evening, videos show the sky already dark from the ash cloud.
Tonga's King Tupou VI was evacuated from the palace, RNZ said, citing local media reports of a convoy of police and troops rushing the monarch to a villa at Mata Ki Eua.
MORE: Videos show flooding, damage after tsunami waves hit San Francisco Bay Area
Telecommunications were affected, though it's not clear how widespread the damage is yet, Ardern said, adding that the main undersea cable has been impacted likely due to loss of power.
The New Zealand government has committed an initial $340,000 in relief supplies, technical support, and supporting local responses, with the country's Defence Force sending assistance to Tonga, Ardern said.
She added that while conditions in the area seem stable, further eruption activity cannot be ruled out.
Waves seen in the US
The eruption also sent waves to the US West Coast, with some exceeding 3 and 4 feet in height, according to the National Weather Service office in San Diego.
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 Harbor northwest of Los Angeles.
The highest waves recorded were in Port San Luis, California (4.3 feet); King Cove, Alaska (3.3 feet); Area Cove, California (3.7 feet); Crescent City, California (3.7 feet); and Port Reyes, California (2.9 feet).
The first tsunami waves were felt on the West Coast early Saturday morning, according to Dave Snider, the tsunami warning coordinator at the National Weather Service's National Tsunami Warning Center in Palmer, Alaska.
A wave as high as 1.2 feet had been observed in Nikolski, Alaska, he told CNN via telephone, while waves as tall as 1 foot were observed in Atka, Adak and King Cove, Alaska.
"This may not be the largest wave as this is coming in yet," Snider told CNN, saying the event was not over.
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The initial coastal tsunami advisory included the states of California, Oregon, Washington and Alaska, according to the National Tsunami Warning Center. All of the advisories had been lifted by early Sunday morning, according the Tsunami Warning Center.
The Pacific Tsunami Warning tweeted no damage was reported thus far from the tsunami observed in the Hawaiian Islands. A tsunami advisory for Hawaii was canceled by the agency Saturday morning.
Adam Weintraub, a spokesperson for the Hawaii Emergency Management Agency, told CNN there were "no reports of major damage so far," though the effects had been felt across multiple islands. Officials were still assessing the damage.
The impacts were the equivalent of a "high King Tide," Weintraub said earlier, telling CNN there had been flooding in parking lots and harbor areas he characterized as "nuisance flooding."
Speaking by telephone, Snider said, "We don't have a really good forecast because this event is based on a volcano rather than an earthquake."
Nonetheless, the National Weather Service in Seattle urged caution along the US Pacific Coast on Saturday. "Move off the beach and out of harbors and marinas in these areas," NWS Seattle tweeted.
The city of Laguna Beach, California, closed all beaches, boardwalks, harbors and piers until further notice in response to the tsunami advisory early Saturday morning, telling residents, "please stay out of the water and away from the shore."
Santa Cruz, California, also experienced some "minor flooding" at the harbor, city manager Elizabeth Smith told CNN.
The waves came right at high tide, Fire Chief Rob Young said. The initial wave occurred at approximately 7:40 a.m. local time, he said, bringing with it a 1 to 2-foot wave right at the peak of high tide. The largest wave came in at about 8:49 a.m. local time, prompting a surge of about 7 feet at the harbor. A subsequent surge just after 10 a.m. was "diminished."
"When it comes, it comes quickly," he said. "Not just a 1-foot wave, but it comes in a surge because it draws all the water out first, and then it comes in."
There was some damage in the harbor and to some docks, he said. There was also "light flooding" on the beaches and up to the city's first surface street, Young said.
All beaches and the harbor will be closed until at least noon local time, Smith said, and people were evacuated from nearby stores and the area near the harbor, though no one has been evacuated from their homes. A surf contest has been postponed and is expected to resume later Saturday.
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