New Zealand and Australian authorities have sent aircraft to the pacific island to assess the damage as searches continue for Angela Glover, who lives in Tonga, after she was reportedly swept away by 4ft waves.
The eruption covered the area in ash, cut power and severed communications. No deaths have been reported so far.
Citing the International Federation of Red Cross and Red Crescent Societies (IFRC), the BBC reported up to 80,000 people could be affected.
New Zealand prime minister Jacinda Arden reportedly said the tsunami has wreaked "significant damage".
It was triggered by the eruption of an underwater volcano which could be heard "more than a thousand miles away".
