The eruption this month of an underwater volcano near Tonga was hundreds of times more powerful than the Hiroshima atomic bomb, according to NASA.

Video above: Tonga Eruption Was So Explosive It Sent Atmospheric Gravitational Waves Into Space

Jim Garvin, chief scientist at NASA's Goddard Space Flight Center, said the eruption of the Hunga-Tonga-Hunga-Ha'apai volcano on Jan. 15 released "hundreds of times the equivalent mechanical energy of the Hiroshima nuclear explosion," referring to one of two atomic bombs dropped by the United States on Japan during World War II.

"This is a preliminary estimate, but we think the amount of energy released by the eruption was equivalent to somewhere between 4 to 18 megatons of TNT," Garvin said on NASA's Earth Observatory website.

In comparison, scientists estimate the 1980 Mount St. Helens eruption released 24 megatons of energy, and Krakatoa — one of the biggest volcanic events in history — erupted in 1883 with 200 megatons, according to NASA.

The eruption near Tonga sent volcanic material surging as high as 25 miles into the atmosphere and generated tsunami waves up to 49 feet high that hit parts of the archipelago including the Pacific nation's main island.

A volcanic cloud extended to cover all of the country's roughly 170 islands, according to Tonga's Prime Minister, impacting the entire population of more than 100,000 people.

Garvin and a team of international researchers evaluated changes in land mass of the volcano since 2015, when an eruption connected two pre-existing islands, Hunga Ha'apai and Hunga Tonga, into one land mass.

Following the eruption this month, all of the new land has gone along with "large chunks" of the two pre-existing islands, the researchers said.

The eruption and tsunami killed at least three people, destroyed hundreds of homes and left remote islands cut off from the world with no communications. Photos show entire island communities blanketed by thick volcanic ash and debris.

Aid agencies and Tongan politicians warned of potential food shortages after crops were ruined by the ash as rescue workers raced to deliver safe drinking water to the islands.

The first contactless aid flights arrived in Tonga last week, with the coronavirus-free nation taking precautions to keep the virus out.

WELLINGTON, New Zealand — New Zealand and Australia have sent military surveillance flights to assess the damage in Tonga caused by Saturday's huge undersea volcanic eruption.

Communications with the Pacific island nation have remained limited since the eruption. The blast likely severed the single underwater cable that provides internet and international phone service.

No casualties have been confirmed on Tonga, although a British woman is reported missing. Officials in nearby countries have warned that casualty numbers could skyrocket once communication is re-established.

"Communication with Tonga remains very limited. And I know that is causing a huge amount of anxiety for the Tongan community here," New Zealand Prime Minister Jacinda Ardern said.

Residents who got messages out to the world described a moonscape left by tsunami waves and volcanic ash fall.

The ash was contaminating drinking water, and New Zealand is planning to fly water and other supplies to Tonga on Tuesday.

According to CNN, the blast on Saturday was likely the most violent eruption the world has seen in three decades. Following the explosion, tsunami advisories briefly went out across the Pacific Rim from Japan to Southern California to South America.

"The eruption was very powerful. There are reports it was heard as far as Alaska," Wendy K. Stovall, a member of the USGS Volcano Hazards Program, told KPIX-TV in San Francisco.

WELLINGTON, New Zealand — The tsunami threat around the Pacific from a huge undersea volcanic eruption has begun to recede, while the extent of damage to Tonga remains unclear.

The eruption on Saturday sent tsunami waves swirling around buildings and people rushing to higher ground. There were no immediate reports of injuries or damage because all internet connectivity with Tonga was lost.

Following the eruption, a tsunami advisory was issued for Japan, Hawaii, Alaska and the U.S. Pacific coast.

Authorities in Southern California closed beaches and piers as a precaution.

The Hunga Tonga Hunga Ha’apai volcano is located about 40 miles north of Tonga's capital.

Video posted to social media shows large waves washing ashore in coastal areas, swirling around homes and buildings. Satellite images show a 3-mile-wide plume of ash, steam and gas rising up into the air 12 miles high.

Tonga's King Tupou VI was reportedly evacuated from his palace near the shore, among the many residents who headed for safety.

About 105,000 people live in Tonga.

A series of eruptions in 2014 and 2015 disrupted international air travel to the Pacific archipelago for several days.

An undersea volcano erupted in spectacular fashion near the Pacific nation of Tonga on Saturday, sending large waves crashing across the shore and people rushing to higher ground.

There were no immediate reports of injuries or the extent of the damage as communications with the small nation remained problematic. Video posted to social media showed large waves washing ashore in coastal areas, swirling around homes and buildings.

New Zealand's military said it was monitoring the situation and remained on standby, ready to assist if asked.

Satellite images showed a huge eruption. The Tonga Meteorological Services said a tsunami warning was in effect for all of Tonga. Authorities in the nearby island nations of Fiji and Samoa also issued warnings, telling people to avoid the shoreline due to strong currents and dangerous waves.

The Islands Business news site reported that a convoy of police and military troops evacuated Tonga's King Tupou VI from his palace near the shore. He was among the many residents who headed for higher ground.

The explosion of the Hunga Tonga Hunga Ha’apai volcano was the latest in a series of spectacular eruptions.

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.”

Earlier, the Matangi Tonga news site reported that scientists observed massive explosions, thunder and lightning near the volcano after it started erupting early Friday.

The site reported that satellite images show a plume of ash 3 miles wide, along with steam and gas rising up into the air to about 12 miles.

More than 1,400 miles away in New Zealand, officials were warning of storm surges from the eruption.

The National Emergency Management Agency said some parts of New Zealand could expect “strong and unusual currents and unpredictable surges at the shore following a large volcanic eruption.”

Late Saturday, the Pacific Tsunami Warning Center said the threat to American Samoa appeared to have passed, although minor sea fluctuations could continue.

The volcano is located about 40 miles north of the capital, Nuku’alofa. Back in late 2014 and early 2015, a series of eruptions in the area created a small new island and disrupted international air travel to the Pacific archipelago for several days.

Tonga is home to about 105,000 people.