Alistair Coldrick, who runs whale watching tours on the island of Vava'u, told Sky News he and his family fled to higher ground after hearing the explosion.

He said: "We knew something catastrophic had happened."

Images show island covered in ash from Hunga-Tonga-Hunga-Ha'apai volcano

"We knew we had to get away from the water. We knew this was really bad, we just didn't know how bad," he added.

Military surveillance flights have been sent from Australia and New Zealand to assess the damage caused by Saturday's eruption from the Hunga-Tonga-Hunga-Ha'apai volcano.

Tonga is comprised of 176 islands, only 36 of them inhabited, with a population of just over 104,000 people. It has been largely cut off from the world after an undersea communication cable was severed - repairs will take some time and there is still volcanic activity in the area.

The tsunami warning system went down following the initial blast, Mr Coldrick said, adding: "Communications were completely severed, but everyone knew this was so drastic that people did move away from the water."

He said the island he is living on is in "fearful limbo" as they wait for communications to be restored: "There has been this general sense of shock because we are kind of in the dark because there is no effective communication between the islands.

Entire islands destroyed as devastation revealed

"We are worried about people on the main island."

Vava'u, which is several hundred kilometres away from the main island of Tonga, had a "light dusting of ash" from the volcano.

"On Monday, people were walking around wearing masks. It was the first time during this pandemic we have had to wear a mask here," said Mr Coldrick.

The government has confirmed three deaths - two locals and British national Angela Glover - in its first official update since Saturday's volcanic eruption and tsunami.

A 65-year-old woman on Mango and a 49-year-old man on Nomuka are the other confirmed deaths, while a number of injuries were also reported.