Gordon_R
Honorary Master
Get away from shore - US and Japan warn on tsunami
Both countries advise people on the coast to move away from water after waves cross ocean from South Pacific.
Social media footage from Tonga showed waves washing through a church and several homes. Witnesses said ash is falling over the capital, Nuku'alofa.
Residents of the Pacific island have been urged to move to higher ground.
It is the latest in a series of eruptions of the Hunga Tonga-Hunga Haʻapai volcano.
The eight-minute eruption was so violent it could be heard as "loud thunder sounds" in Fiji, more than 800km away, officials in the capital Suva said.
The plumes of gas, smoke and ash pouring from the volcano reached 20km into the sky, said Tonga Geological Services.
The Hunga Tonga-Hunga Ha'apai lies about 65km north of the Tongan capital.

