Prime Minister Scott Morrison has vowed to give Tonga every possible support after a devastating tsunami hit the Pacific island nation.
Australia will send a P-8 plane to Tonga on Monday to help assess damage in the country.
The tsunami, caused by an underwater volcano eruption on Saturday, has caused severe damage to communications in Tonga, making it difficult to determine how critical infrastructure has fared.
Mr Morrison said the communication disruption and ash clouds made the situation challenging.
"We're working to get as much support to Tonga as we possibly can," he told 2GB on Monday.
"They're part of our Pacific family, and ... like all of those island nations, we're always there to support and we certainly will be on this occasion.
All Australians and other officials in Tonga have been accounted for.
Defence forces and foreign affairs officials will be working with other countries in the region to provide support.
Mr Morrison has also spoken with his New Zealand counterpart Jacinda Ardern.
The P-8 plane is set to reach Tonga on Monday morning, and is part of a coordinated response by Australia and New Zealand.
Pacific Minister Zed Seselja said while there were reports of significant property damage in Tonga, there have been no reports of mass casualties.
"There is still very limited, if any, information coming from the outer islands, and so that will be the focus in coming hours," Senator Seselja told ABC TV.
"We hope that in the next several hours, we'll have a much better assessment of the damage in those outer islands where communications continue to be cut off."
Senator Seselja said other support measures were being prepared and ready to go, including a C-130 plane with humanitarian supplies.
HMAS Adelaide, currently in Sydney, is being deployed to Brisbane where it will be loaded with supplies for Tonga.
"We've been chatting to our US, New Zealand and French partners and others about how we can get a coordinated response going," Senator Seselja said.
"There will be further discussions with the Tongan government to determine how we can support the people of Tonga at this very difficult time, but we stand by to do much more."
A Department of Foreign Affairs spokesman said there were early reports of substantial ash coverage through the Tongan capital of Nuku'alofa along with coastal inundation and damage to infrastructure.
Foreign Minister Marise Payne said the government was in contact with the high commissioner in Tonga, but communication was limited.
"This is a very challenging time. Communications are deeply, deeply affected by the events of the volcanic eruption. It has been felt in other parts of the region," she told reporters on Monday.
"We're seeking further information about the extent of the damage outside of (the capital) Nuku'alofa."
- Those concerned about Australian citizens in Tonga should contact DFAT on 1300 555 135 or +61 2 6261 3305.
Communications still cut off
There are no official reports of injuries or deaths in Tonga as yet but communications are still limited and outlying coastal areas remain cut off.
Satellite images show some of the outlying islands submerged.
A UK woman has reportedly gone missing after she was washed away, media reports said.
Angela Glover and her husband James, who own the Happy Sailor Tattoo in Nuku'alofa, had gone to get their dogs when the wave hit. James managed to hold onto a tree but his wife, who also runs a dog rescue on the island, and their dogs were washed away, New Zealand state broadcaster TVNZ reported. Several social media posts from family and friends said she has still not been found.
The eruption on Saturday was so powerful it was recorded around the world, triggering a tsunami that flooded Pacific coastlines from Japan to the United States.
The capital Nuku'alofa suffered "significant" damage, New Zealand Prime Minister Jacinda Ardern said, adding there had been no reports of injury or death but a full assessment was not yet possible with communication lines down.
"The tsunami has had a significant impact on the foreshore on the northern side of Nuku'alofa with boats and large boulders washed ashore," Ms Ardern said after contact with the New Zealand embassy in Tonga.
"Nuku'alofa is covered in a thick film of volcanic dust but otherwise conditions are calm and stable."
Tonga was in need of water supplies, she said: "The ash cloud has caused contamination."
At least 80,000 people expected to be affected
Red Cross said it was mobilising its regional network to respond to what it called the worst volcanic eruptions the Pacific has experienced in decades.
“Red Cross has enough relief supplies to support 1,200 households with essential items such as tarpaulins, blankets, kitchen sets, shelter tool kits and hygiene kits,” said Katie Greenwood, IFRC’s Pacific Head of Delegation told Reuters.
Ms Greenwood said the agency is expecting up to 80,000 people to be affected by the tsumani
"That is what we are planning for as a worst case scenario until we can get further confirmation from the people on the ground," she said.
The agency said there were concerns that communities may not have access to safe drinking water as a result of saltwater inundation caused by the tsunami waves and ashfall.
A police officer patrols the beach as waters recede in front of the Santa Cruz Beach Boardwalk in Santa Cruz, Calif., Saturday, 15 January, 2022. Source: FR171100 AP
The United States was "deeply concerned for the people of Tonga", Secretary of State Antony Blinken said, pledging support for the island nation.
World Health Organization chief Tedros Adhanom Ghebreyesus tweeted that the WHO was "ready to support the government and provide help to the people affected".
The United Nations children's agency said it was preparing emergency supplies to fly into Tonga in coordination with Australia and New Zealand.
A 1.2-metre wave swept ashore in the Tongan capital with residents reporting they had fled to higher ground, leaving behind flooded houses, some with structural damage, as small stones and ash fell from the sky.
"It was massive, the ground shook, our house was shaking. It came in waves. My younger brother thought bombs were exploding nearby," resident Mere Taufa told the Stuff news website Saturday.
She said water filled their home minutes later and she watched the wall of a neighbouring house collapse.
"We just knew straight away it was a tsunami. Just water gushing into our home," Ms Taufa said.
"You could just hear screams everywhere, people screaming for safety, for everyone to get to higher ground."
Tonga's King Tupou VI was reported to have been evacuated from the Royal Palace in Nuku'alofa and taken by police convoy to a villa well away from the coastline.
Dramatic satellite images showed the long, rumbling eruption of the Hunga Tonga-Hunga Ha'apai volcano spew smoke and ash in the air, with a thunderous roar heard 10,000 kilometres away in Alaska.
The eruption triggered tsunamis across the Pacific with waves of 1.74 metres measured in Chanaral, Chile, more than 10,000 kilometres away, and smaller waves seen along the Pacific coast from Alaska to Mexico.
In California, the city of Santa Cruz was hit by flooding due to a tidal surge generated by the tsunami, videos retweeted by the US National Weather Service showed.
Two women drowned on a beach in northern Peru due to "anomalous waves" registered after the volcanic eruption in Tonga, more than 10,000 kilometers away, local emergency services said on Sunday.
The two women drowned on Saturday in Lambayeque.
Peru's government on Saturday closed 22 Pacific ports in the country's north and centre due to the waves.
The centre for national emergency operations said the unusually strong waves were "due to the volcanic activity in north Nuku'alofa, Tonga."
By 0300 GMT on Sunday, the Pacific Tsunami Warning Center in Hawaii said the threat from the eruption had passed.
Heard in Alaska
The US Geological Survey recorded Saturday's eruption as equivalent to a 5.8-magnitude earthquake at zero depth.
The volcano's eruption lasted at least eight minutes and sent plumes of gas, ash and smoke several kilometres into the air.
New Zealand scientist Marco Brenna, a senior lecturer at Otago University's School of Geology, described the impact of the eruption as "relatively mild" but said another eruption with a much bigger impact could not be ruled out.
The eruption was so powerful it was even heard in Alaska, the UAF Geophysical Institute tweeted.
"A part of the pressure signal in Alaska was in the audible range. The very large signal is not that surprising considering the scale of the eruption, but the audible aspect is fairly unique," it said, citing Alaska Volcano Observatory scientist David Fee.
"He recalls only a couple other volcanic eruptions doing something like this: Krakatau and Novarupta," it tweeted. This referred to the 19th-century eruption of Indonesia's Krakatau, and Alaska's Novarupta, the most powerful volcanic eruption of the 20th century.
The Fife weather station in Scotland tweeted it was "just incredible to think of the power that can send a shockwave around the world" after the eruptions produced a jump in its air pressure graph.
Hunga-Tonga-Hunga-Ha'apai, which lies about 65 kilometres north of Nuku'alofa, has a history of volatility.
In recent years, it breached sea level during a 2009 eruption while in 2015 it spewed so many large rocks and ash into the air that when they settled a new island had formed two kilometres long by one kilometre wide and 100 metres high.