A strong 6.5-magnitude earthquake has struck off the Pacific nation of Tonga, the US Geological Survey says, but there has been no immediate tsunami warning or reports of significant damage.

The undersea quake hit 71 kilometres northeast of the Tongan capital Nuku’alofa at a shallow depth of 10 kilometres on Saturday, the USGS said.

Residents reported a “short, very violent” jolt at around 0600 GMT (1600 AEST) that knocked items off shelves and sent people fleeing for higher ground, though there was no indication of a tsunami.

The Hawaii-based Pacific Tsunami Warning Center did not issue an alert, and the USGS said there was a low likelihood of casualties and damage.

Geoscience Australia estimated the tremor at a magnitude 6.3 and said it was likely to have been felt within a wide radius but damage was unlikely.

Tonga sits on the so-called Pacific Ring of Fire, a region of frequent seismic activity due to collisions between continental plates.