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.

Where is Tonga's Hunga-Tonga-Hunga-Ha'apai volcano?

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.

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.

Where did the tsunami hit?

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.

What is happening with the ash cloud?

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.

What is the scale of devastation?

At least two people, including a British national who lived in Nuku'alofa, were killed in Tonga following the eruption and tsunami.

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.

"From what little updates we have, the scale of the devastation could be immense, especially for outer lying islands," said Katie Greenwood, IFRC's Pacific Head of Delegation, according to Reuters.

New Zealand's Defense Force dispatched an Orion aircraft for Tonga on a surveillance mission to assess the damage. Ardern said the country has committed an initial $340,000 in relief supplies, technical support, and supporting local responses.

Australia said it is preparing for additional support, with a plane loaded with humanitarian supplies such as water and sanitation kits, ready to deliver to Tonga once conditions allow.

China and the self-ruled island of Taiwan said in separate statements they are willing to provide assistance at Tonga's request.

Correction: A previous version of this timeline incorrectly stated the number of times the volcano erupted. It was twice.