Experts have warned that the Hunga Tonga-Hunga Ha'apai volcano eruption means the volcano may be unstable and has an increased risk of more tsunamis.
The underwater volcano erupted in the Pacific last week and was heard as far as the US, triggering a 7.4 magnitude earthquake, sending a tsunami towards Tonga.
The Red Cross has warned that up to 80,000 people could be impacted by the natural disaster. However, the full extent of damage caused is yet to be determined as information from the island is scarce.
New Zealand has sent a plane to assess the situation, with Prime Minister Jacinda Ardern saying the tsunami caused "significant damage".
Auckland University professor, Shane Cronin, said studies of eruptions of the volcano in 200AD and 1100AD suggested it would likely remain active for a significant amount of time.
Prof Cronin said the force of the blast caused by the eruption means the volcano's caldera has most likely been altered and may be unstable.
He said: "The eruption episode could last several weeks or months."
Tonga, which has a population of about 105,000 people, was sent into panic as people fled to higher ground in attempts to escape the destruction.
Residents are currently completely cut off from the rest of the world after phone lines and the internet were cut.
On Saturday, the volcanic blast seriously damaged the capital Nuku'alofa and severed an undersea communications cable that could take up to two weeks to restore.
Southern Cross Cable Network's networks director Dean Veverka said: "We're getting sketchy information, but it looks like the cable has been cut.
"It could take up to two weeks to get it repaired. The nearest cable-laying vessel is in Port Moresby," more than 4,000km from Tonga.
Southern Cross is assisting Tonga Cable Limited, which owns the 872km cable linking the island nation with Fiji.
This is not the first time this has happened, as Tonga was isolated for two weeks in 2019 when a ship's anchor cut the cable.
The Tonga Meteorological Agency had also warned that the smell of sulphur and ammonia had been reported in some areas.
