On Tuesday, New Zealand's Foreign Ministry warned further eruptions of the volcano were likely, posing a tsunami risk.

The estimation was based on modeling by GNS Science, a New Zealand geological research institute, the ministry said. "The most likely scenario is for ongoing eruptions in the next several days to weeks, with ongoing tsunami risk to Tonga and New Zealand," it said.

The eruption on Saturday generated tsunami waves up to 49 feet (15 meters) high that hit the west coast of Tonga's main island, Tongatapu, and the 'Eua and Ha'api islands.

A United Nations spokesperson said an initial assessment by Tongan authorities found 100 houses were damaged and 50 destroyed on Tongatapu, the country's main island, home to the majority of the population. No evacuation centers are open on the main island, and people who were displaced are mostly staying with extended families.

On 'Eua, 89 people are in evacuation centers, the spokesperson said, adding that information from outer islands remains scarce.

Race to deliver aid to Tonga

Photos show entire island communities that were once lush and green, now blanketed by thick, gray ash. Many homes appear damaged or completely destroyed.

Widespread stagnant pools of salt water, coupled with the volcanic ash, are polluting drinking water sources, according to the Red Cross.

The delivery of aid was hampered by ashfall covering Tonga's Fua'amotu International Airport runway, forcing New Zealand to send two navy ships to assist with recovery -- but they will not arrive until Friday.

Yutaro Setoya, the official in charge of the WHO liaison office for Tonga, said he believed the first aid flights could arrive on Thursday.

He also described the the conditions in the wake of the disaster.

"After the eruption initially, there was a sound on the roof like rain, and it was not actually a rain. It was small pellets falling from the sky," Setoya told CNN on Wednesday. The pellets were followed by very fine ash, which by the time Tonga woke up the next day resembled "gray snow like two centimeters everywhere."

With cleanup efforts underway, rescue workers are racing to deliver safe drinking water to the island nation as it grapples with the shortages.

"Securing access to safe drinking water is a critical immediate priority," said Katie Greenwood, the Pacific Head of Delegation for the International Federation of Red Cross and Red Crescent Societies, pointing to the mounting risk of diarrhea and diseases such as cholera.

Covid risk

The World Health Organization (WHO) will not send international aid teams to Tonga due to the risk of bringing Covid-19 into the community, according to Sean Casey, WHO's Pacific Covid-19 incident manager.

Tonga has done "extremely well" on their vaccine rollout with more than 80% fully inoculated, Casey said. The country shut its borders to international travelers near the start of the pandemic, and has used this time to prepare its population and health care systems for an outbreak, he added.

"We have lots of natural disasters in this part of the world and you don't want to have to deal with multiple emergencies at the same time, if that can be avoided," Casey said.

WHO is still working to send supplies to Tonga, including telecommunication tools such as satellite phones, water sanitation equipment and materials to repair and build shelters.

"Everybody in Tonga, every family in town is affected by this," Casey said. "That's always the case in the Pacific. The numbers look very small, but the impact proportionately on a very small country is massive."

Tonga's government has not requested aid from WHO, according to the UN health agency.

Tonga is largely cut off from the world

Tonga's communication systems remain severely limited after damage to a key undersea cable cut international and inter-island calls, New Zealand's Foreign Ministry said Tuesday.

According to the ministry, an international mobile network provider has set up an interim system on Tongatapu using a satellite dish, which could restore 2G connections. But this "will be limited and patchy," the ministry said.

Many Tongans living outside the country now face a daunting wait to reconnect with loved ones at home, as rescue workers try to salvage the underwater cable.

Repairs are not expected to begin until February 1, and it may take a further two weeks after that to restore the cable, according to a company assisting with the work.

"Just received word that our family on the main island of Haapai is safe and that our Ha'apai home 'Fuino' is still standing! Its over 100 years old and has been through many cyclones and now a tsunami," Taufatofua said Wednesday. "Still no word from my Father or our family on Kotu and surrounding lower islands."

Tongan-Australian artist and activist Seini Taumoepeau told Reuters her "worst fear is always that you're not going to see the people that you love again," adding she has had no contact with anyone from Tonga since before the tsunami hit.

The Hunga-Tonga-Hunga-Ha'apai volcano, about 20 miles (30 kilometers) southeast of Tonga's Fonuafo'ou island, sits underwater between two small islands at about 6,500 feet (2,000 meters) high from the sea floor, with about 328 feet (100 meters) 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 7.5 miles (12 kilometers) into the air. The volcano erupted again on January 14 and the massive eruption on January 15 sent shockwaves around the world and triggered tsunami waves that were felt thousands of miles away, killing at least two people in Peru.