The Hunga Tonga-Hunga Ha'apai volcano, which erupted on Saturday, was about 65km north of Tonga's capital Nuku'alofa.
There is now a huge clean-up operation in the town, which has been blanketed in thick volcanic dust.
Serious damage has been reported from the west coast of Tongatapu and a state of emergency has been declared.
The Ministry of Foreign Affairs and Trade has confirmed two deaths so far, but Fiji-based United Nations (UN) co-ordinator Jonathan Veitch said there were still areas that had not been contacted.
