After an underwater volcano off Tonga erupted on Saturday, tsunami warnings were triggered down Australia's east coast while evacuation orders were issued for Lord Howe Island and Japan.
There was a downpouring of ash on the island chain as well as flooding and disruptions to phone and power connections.
There were no immediate reports of injuries or on the extent of the damage because all internet connectivity with Tonga was lost at about 6.40pm local time, Doug Madory, director of internet analysis for the network intelligence firm Kentik said.
The Bureau of Meteorology in Australia said a 1.2 metre tsunami wave had been observed in Nuku'alofa, Tonga's capital.
On Sunday afternoon, the bureau is continuing to monitor the situation and marine threats have been issued for Lord Howe and Norfolk islands offshore as well as parts of Queensland, NSW, Victoria and Tasmania.
Marine warnings were issued along Australia's coast overnight and, in Sydney, the State Emergency Service evacuated Sydney's Bondi Beach.
On Norfolk island waves of 1.27m waves were observed and on Lord Howe Island they were measured at 1.10m.
The Islands Business news site reported that a convoy of police and military troops moved Tonga's King Tupou VI from his palace near the shore.
He was among the many residents who headed for higher ground.
Satellite images showed a huge eruption, a plume of ash, steam and gas rising like a mushroom above the blue Pacific waters.
The New Zealand Defence Force said it was monitoring the situation in Tonga and stood ready to assist if requested by the government but that so far no request had been made, according to Radio New Zealand.
A spokesperson for the Australian government said initial assessments are underway and the Department of Foreign Affairs is working to ensure Australians in Tonga are safe and accounted for.
"Tonga is part of our Pacific family and our thoughts are with the entire community dealing with the impact of the volcanic eruption and tsunami," the spokesperson said in a statement.
"The Prime Minister and Minister for Foreign Affairs are monitoring the situation and Australia stands ready to provide support to Tonga if requested."
Authorities across the Pacific, including in Samoa, Fiji and New Zealand, issued tsunami alerts, warning people to stay away from coastal areas due to the possibility of strong and unusual currents and unpredictable surges.
"People in or near the sea should move out of the water, off beaches and shore areas and away from harbours, rivers and estuaries," the New Zealand National Emergency Management Agency warned.
Hauraki Gulf Weather recorded a 71 centimetre wave at Great Barrier Island, near Auckland following the eruption.
The volcano is located about 2000 kilometres northeast of New Zealand.
New Zealand's MetService said its instruments detected a pressure surge from the eruption.
New Zealanders took to social media to report they could hear the eruption.
Fiji issued a tsunami warning, urging residents to avoid the shorelines "due to strong currents and dangerous waves".
Jese Tuisinu, a television reporter at Fiji One, posted a video on Twitter showing large waves crashing ashore, with people trying to flee in their cars.
"It is literally dark in parts of Tonga and people are rushing to safety following the eruption," he said.
Residents of American Samoa were alerted to a tsunami warning by local broadcasters as well as church bells that rang territory-wide as an outdoor siren warning system was out of service.
In Hawaii, the PTWC reported waves that measured half a metre in Nawiliwili, Kauai and 80cm in Hanalei.
The National Weather Service said there were reports of boats getting pushed up in docks but the hazard diminished as the morning went on.
The Japan Meteorological Agency said there may be a slight swelling of the water along the Japanese coasts but it was not expected to cause any damage.
The volcano also erupted on Friday, when small tsunami waves of up to 30cm were recorded, the Tonga Meteorological Office said.
The volcano was erupting intermittently in late December but Friday's eruption was about seven times more powerful than the previous eruption, Tonga Geological Services said.
Australian Associated Press