(CNN)The eruption of an underwater volcano near Tonga on Saturday was likely the biggest recorded anywhere on the planet in more than 30 years, according to experts.
Dramatic images from space captured the eruption in real time, as a huge plume of ash, gas and steam was spewed up to 20 kilometers (12.4 miles) into the atmosphere -- and tsunami waves were sent crashing across the Pacific.
The eruption and subsequent tsunami caused "significant damage" along the western coast of the main island of Tongatapu, the New Zealand High Commission in Nuku'alofa said Monday.
"A thick layer of ash remains across Tongatapu," the statement said.
On social media, footage showed people fleeing as waves inundated Tonga's capital, Nuku'alofa, and the afternoon sky turned pitch black due to the heavy ash cloud. Tsunami waves were also recorded thousands of miles away along the United States' West Coast, in Peru, New Zealand and Japan. In Peru, at least two people died after being swept up by high waves.
At least two deaths have been reported and aid organizations are concerned about contaminated air and access to clean water for people in Tonga's outlying islands.
With communications down, Australia and New Zealand sent flights to survey the damage.
Here's what we know about the eruption and fallout.
Tonga is a Polynesian country of more than 170 South Pacific islands and home to about 100,000 people. It's a remote archipelago that lies about 800 kilometers (500 miles) east of Fiji and 2,380 kilometers (1,500 miles) from New Zealand.
The Hunga-Tonga-Hunga-Ha'apai volcano, about 30 kilometers (20 miles) southeast of Tonga's Fonuafo'ou island, sits underwater between two small islands at about 2,000 meters (6,500 feet) high from the sea floor, with about 100 meters (328 feet) visible above sea level.
Researchers said it has erupted regularly over the past few decades.
In 2009, an eruption sent plumes of steam and ash into the air and formed new land above the water, and an eruption in January 2015 created a new island about 2 kilometers wide -- effectively joining up Hunga-Tonga and Hunga-Ha'apai islands.
The most recent eruption began in December 2021, with gas, steam, and ash plumes rising about 12 kilometers (7.5 miles) into the air. The volcano erupted again on January 14 and a massive eruption on January 15 sent shockwaves around the world and triggered tsunami waves across the Pacific.
The eruption caused a tsunami on Tonga's largest island, Tongatapu, with waves recorded at 1.2 meters (about 4 feet) near Nuku'alofa city flowing onto coastal roads and flooding properties on Saturday.
Tsunami warnings went into effect across Pacific Island nations including Fiji, Samoa and Vanuatu. Footage from the ground in Fiji shows people fleeing to higher ground in the capital, Suva, as large waves hit the coast.
Tsunami warnings and advisories were also issued from parts of New Zealand, Japan and Peru, to the United States and Canada's British Columbia.
In Japan, the northeastern prefecture of Iwate saw waves as high as 2.7 meters (9 feet) and multiple smaller tsunamis were reported in numerous other locations, according to public broadcaster NHK. By Sunday afternoon, all tsunami advisories had been lifted in Japan.
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. Tsunami waves were felt in California, Alaska and Hawaii.
A giant volcanic ash cloud blanketed Tonga over the weekend, turning the afternoon sky dark and coating Nuku'alofa in a thick foam of volcanic dust on Saturday.
Save the Children said drinking water supplies could be contaminated by the ash and smoke and the immediate concern in Tonga is for air and water safety.
The ash cloud was drifting westwards and was visible over Fiji, Vanuatu and New Caledonia on Sunday. By Monday it had reached Australia's Queensland, according to the state's meteorological service.
"If you noticed a particularly stunning sunrise, it was the sunlight being scattered by #Volcanic ash from the eruption over in #Tonga," Queensland's Bureau of Meteorology said on Twitter.
The ash prevented an Australian reconnaissance flight from departing to assess the damage in the early hours of January 17, though the flight did take off later that morning.
Several flights from Australia, New Zealand and Fiji to Tonga were postponed due to the ash cloud.
Early data suggests the volcanic eruption was the biggest since the 1991 blast at Mount Pinatubo in the Philippines, New Zealand-based volcanologist Shane Cronin told Radio New Zealand.
"This is an eruption best witnessed from space," Cronin said, according to Reuters.
"The large and explosive lateral spread of the eruption suggests that it was probably the biggest one since about the 1991 eruption of Pinatubo," Cronin said.
At least two people, including a British national who lived in Nuku'alofa, were killed in Tonga following the eruption and tsunami.
The first images to emerge of the aftermath on January 18 show a thick layer of ash covering entire communities, but the extent of the damage remains unknown as communications -- particularly on the outlying islands -- have not yet been reestablished.
Tonga "needs immediate assistance to provide its citizens with fresh drinking water and food," the country's Speaker of the House Lord Fakafanua said in a statement posted to social media.
He said "many areas" had been affected by "substantial volcanic ashfall" but "the full extent of the harm to lives and property is currently unknown."
New Zealand's Prime Minister Jacinda Ardern said on January 16 that tsunami waves had a "significant impact" on Nuku'alofa, with boats and large boulders washed ashore. "Shops along the coast have been damaged and a significant cleanup will be needed," she said.
The main undersea communications cable has also been impacted, likely due to loss of power.
Australia's Minister for International Development and the Pacific, Zed Seselja, said there was "significant property damage" in Tonga, including to roads and houses. He said there is still "very limited, if any" information coming from the outer islands.
New Zealand's High Commission in Nuku'alofa echoed this, saying in a statement Monday that "significant" damage has been reported along the western coast of Tongatapu.
A family-owned beach resort located on Tongatapu also said the business had been destroyed. "It's with sadness to say that our beautiful home Ha'atafu beach resort has been completely wiped out. The whole western coastline has been completely destroyed along with Kanukupolu village," the Ha'atafu Beach Resort posted on Facebook on Monday.
The International Federation of Red Cross and Red Crescent Societies said its teams are on the ground and have enough supplies in the country to support 1,200 households.