Angela Glover was at her home with her husband, James, and their dogs when the tsunami triggered by volcanic eruption hit their house in the low-lying Veitongo area.
Mr Glover was able to hold on to a tree as waves as high as 4 foot (1.2 metres) hit their home. Ms Glover however, was swept away by the water, her family and friends said.
“The tsunami hit around 5.30pm local time, I believe,” her brother, Nick Eleini told The Guardian. “Angela and her husband, James, got washed away. James was able to cling on to a tree for quite a long time, but Angela was unable to do so and was washed away with the dogs, I think four or five dogs.”
Ms Glover, who was born in Brighton, runs an animal shelter and also works at a tattoo parlour in Tonga’s capital, Nuku’alofa.
Mr Eleini, who is flying home from Sydney to be with their mother in the UK in east Sussex, said one of the dogs has been found in the search and rescue operation but there has been no sign of his sister.
The family has reached out to the local police officials and British embassy in Tonga to find Ms Glover.
Her family learned about what happened only after Mr Glover reached out to them in the UK through a satellite phone supplied by the British embassy.
The Red Cross has been mobilising its response to the worst volcanic eruption the pacific has seen in decades.
Up to 80,000 people are feared affected by the tsunami, said Katie Greenwood, the Pacific head of delegation for the International Federation of Red Cross and Red Crescent Societies.
While the volcano in Hunga-Tonga-Hunga-Ha’apai has erupted frequently in the last few decades, Saturday’s eruption was visible from the space and felt as far away as Fiji, New Zealand, the United States and Japan.
At least two people are reported to have drowned in Northern Peru at a beach after being struck in a high wave due to the tsunami.
Countries spread over thousands of kilometres in the Pacific island and to the west witnessed volcanic ash clouds over them a day after the eruption.
Meanwhile, Australia and New Zealand have sent their surveillance flights on Monday to assess damage on the island.
Initial reports suggest no mass casualties took place after the eruption and tsunami, Australian minister for the Pacific Zed Seselja said.
However significant damage has been reported with “houses thrown around” after police visited the beach areas.