Underwater volcano Hunga-Tonga-Hunga-Ha'apai has erupted again, sending ash, steam and gas 20km into the air.
There is a tsunami warning in place for all the islands of the Kingdom of Tonga as the volcanic activity affects coastal water levels. People are advised to stay out of the water and away from the coast.
The maximum tsunami wave was recorded by the Nuku'alofa tide gauge at 12.30pm and was about 30cm, and sea level fluctuation has been observed.
The volcano is located about 30km south-east of Fonuafo'ou island in Tonga.
Tonga Geological Services head Taaniela Kula said the eruption had a radius of 260km.
It was about seven times more powerful than the last eruption on December 20 last year and continuing to grow, Kula said.
Kula said people on the islands of Tongatapu, Ha'apai and Vava'u needed to stay indoors as much as possible, wear a mask if they were outside and cover rainwater reservoirs and rainwater harvesting systems.
Changes to seawater levels have also been detected on the south coast of Samoa as a result of this morning's eruption.
Ash fall had been witnessed in the islands of Ha'apai and domestic flights were on hold as a result, Kula said.
The volcano erupted intermittently in late December.
The National Emergency Management Agency says there is no warning for New Zealand.