Meanwhile, Tsunami waves measuring 2 feet in height were observed by sea-level gauges at the capital of the US territory of American Samoa following volcanic activity in Tonga, the US-based Pacific tsunami warning center said.
The tsunami threat continues and sea level fluctuations and strong ocean currents pose hazards along beaches in harbors, the tsunami monitor said in a statement.
The eruption was so intense it was heard as "loud thunder sounds" in Fiji more than 800 kilometres (500 miles) away, officials in Suva said.
Victorina Kioa of the Tonga Public Service Commission said Friday that people should "keep away from areas of warning which are low-lying coastal areas, reefs and beaches."
The head of Tonga Geological Services Taaniela Kula urged people to stay indoors, wear a mask if they were outside and cover rainwater reservoirs and rainwater harvesting systems.
The Pacific Tsunami Warning Centre issued a "tsunami advisory" for American Samoa, saying there was a threat of "sea level fluctuations and strong ocean currents that could be a hazard along beaches."
The Hunga Tonga-Hunga Ha'apai volcano sits on an uninhabited island about 65 kilometres (40 miles) north of the Tongan capital Nuku'alofa.