A strong 6.4-magnitude earthquake struck off the Pacific nation of Tonga on Saturday, US seismologists said, but there were no immediate reports of damage and no tsunami warning was issued.

The quake happened at 11:08 PM (1008 GMT) 78 kilometres (49 miles) from the town of Neiafu, on the south coast of the island Vava'u, at a depth of about 130 kilometres (80 miles), the US Geological Survey (USGS) said.

The epicentre of the tremor was 280 kilometres (173 miles) north of the capital Nuku'alofa.

The Pacific Tsunami Warning Centre said in a statement that the quake did not generate a tsunami. The USGS had initially reported it as a 6.7-magnitude quake.

Tonga, almost 2,000 kilometres (1,240 miles) northeast of New Zealand, lies on the so-called Pacific "Ring of Fire", where continental plates collide causing frequent seismic activity.