Strong earthquake hits Tonga, no reports of damage

A strong 6.6 magnitude earthquake has struck the South Pacific island nation of Tonga.

The quake hit about 9.47am local time (6.47am AEST), Geoscience Australia said.

The quake had a preliminary magnitude of 6.6 when it hit, the US Geological Survey said. Its epicentre was 198km north of the capital, Nuku'alofa, at a depth of 112km.

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It's understood tsunami sirens were sounded on the island, but they have since been cancelled.

The Hawaii-based Pacific Tsunami Warning Centre said there was no risk of the quake causing a tsunami.

Tonga sits on the Pacific "Ring of Fire," the arc of seismic faults around the Pacific Ocean where much of the world's earthquake and volcanic activity occurs.

It comes a day after a magnitude 6.4 earthquake struck Vanuatu.