SYDNEY: A strong 6.1-magnitude earthquake struck off the Pacific nation of Tonga Monday, US seismologists said, but no tsunami warning was issued.

The US Geological Survey (USGS) said the quake was shallow, striking 154 kilometres (95 miles) northwest of the village of Pangai, the administrative capital of the Ha'apai group of islands in central Tonga.

The region's homes are vulnerable to earthquake shaking, according to USGS, but it said there was a low likelihood of casualties and damage.

The Pacific Tsunami Warning Center did not immediately issue any warnings.

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