Photo used for illustrative purposes.

A powerful 7.2-magnitude earthquake struck off the Pacific island nation of Tonga on Friday, but no tsunami warning was issued, US monitoring agencies said.

The earthquake struck shortly after 7:00 am (1800 GMT Thursday) at a depth of 167 kilometres (103 miles) some 290 kilometres southwest of the capital Nuku'alofa, the United States Geological Survey said.

Gary Vite, chief meteorologist at the Tonga Meteorological Services told AFP there were no immediate reports of damage.

The Pacific Tsunami Warning Centre said there was no tsunami threat, based on available information.

Veisina Sangusangu, a receptionist at the Little Italy hotel in Nuku'alofa, said the quake lasted about 30 seconds.

"It was stronger than the earthquakes we usually feel. The building shook," she added.

Tonga sits on the Pacific "Ring of Fire", where tectonic plates often shift, frequently experiencing seismic activity.

Agence France-Presse